hash.c

/*
 * MacRuby implementation of Ruby 1.9's hash.c.
 *
 * This file is covered by the Ruby license. See COPYING for more details.
 *
 * Copyright (C) 2012-2013, The MacRuby Team. All rights reserved.
 * Copyright (C) 2007-2011, Apple Inc. All rights reserved.
 * Copyright (C) 1993-2007 Yukihiro Matsumoto
 * Copyright (C) 2000 Network Applied Communication Laboratory, Inc.
 * Copyright (C) 2000 Information-technology Promotion Agency, Japan
 */

#include "macruby_internal.h"
#include "ruby/st.h"
#include "ruby/util.h"
#include "ruby/signal.h"
#include "ruby/node.h"
#include "id.h"
#include "objc.h"
#include "vm.h"
#include "hash.h"
#include "array.h"
#include "class.h"

static VALUE rhash_try_convert(VALUE, SEL, VALUE);

VALUE
rb_hash_freeze(VALUE hash)
{
    return rb_obj_freeze(hash);
}

VALUE rb_cRubyHash;

static ID id_yield;

static SEL selFlattenBang = 0;
static SEL selDefault = 0;
static SEL selHash = 0;

unsigned long
rb_hash_code(VALUE obj)
{
    switch (TYPE(obj)) {
	case T_FIXNUM:
	case T_FLOAT:
	case T_SYMBOL:
	case T_NIL:
	case T_FALSE:
	case T_TRUE:
	    return rb_hash_end(rb_hash_start((unsigned int)obj));

	case T_STRING:
	    return rb_str_hash(obj);

	case T_ARRAY:
	    return rb_ary_hash(obj);
    }

    VALUE v = rb_vm_call(obj, selHash, 0, NULL);
retry:
    switch (TYPE(v)) {
	case T_FIXNUM:
	    return FIX2LONG(v);
	case T_BIGNUM:
	    return ((unsigned long *)(RBIGNUM_DIGITS(v)))[0];
	default:
	    v = rb_to_int(v);
	    goto retry;
    }
}

VALUE
rb_hash(VALUE obj)
{
    return LONG2NUM(rb_hash_code(obj));
}

typedef int st_foreach_func(st_data_t, st_data_t, st_data_t);

struct foreach_safe_arg {
    st_foreach_func *func;
    st_data_t arg;
};

static int
foreach_safe_i(st_data_t key, st_data_t value, struct foreach_safe_arg *arg)
{
    if (key == Qundef) {
	return ST_CONTINUE;
    }
    const int status = (*arg->func)(key, value, arg->arg);
    if (status == ST_CONTINUE) {
	return ST_CHECK;
    }
    return status;
}

void
st_foreach_safe(st_table *table, int (*func)(ANYARGS), st_data_t a)
{
    struct foreach_safe_arg arg;

    arg.func = (st_foreach_func *)func;
    arg.arg = a;
    st_foreach(table, foreach_safe_i, (st_data_t)&arg);
}

static int
rb_any_cmp(VALUE a, VALUE b)
{
    if (a == b) {
	return 0;
    }
    return !rb_eql(a, b);
}

static st_index_t
rb_any_hash(VALUE a)
{
    return (int)rb_hash_code(a);
}

static const struct st_hash_type objhash = {
    rb_any_cmp,
    rb_any_hash,
};

static const struct st_hash_type identhash = {
    st_numcmp,
    st_numhash,
};

static VALUE
rhash_alloc(VALUE klass, SEL sel)
{
    assert(klass != 0);
    assert(rb_klass_is_rhash(klass));

    NEWOBJ(hash, rb_hash_t);
    hash->basic.flags = 0;
    hash->basic.klass = klass;
    GC_WB(&hash->tbl, st_init_table(&objhash));
    hash->ifnone = Qnil;
    hash->has_proc_default = false;
    return (VALUE)hash;
}

VALUE
rhash_dup(VALUE rcv, SEL sel)
{
    VALUE klass = CLASS_OF(rcv);
    while (RCLASS_SINGLETON(klass)) {
	klass = RCLASS_SUPER(klass);
    }
    assert(rb_klass_is_rhash(klass));

    VALUE dup = rhash_alloc(klass, 0);
    rb_obj_invoke_initialize_copy(dup, rcv);

    OBJ_INFECT(dup, rcv);
    return dup;
}

VALUE
rb_hash_new(void)
{
    return rhash_alloc(rb_cRubyHash, 0);
}

VALUE
rb_hash_new_fast(int argc, ...)
{
    assert(argc % 2 == 0);

    VALUE hash = rhash_alloc(rb_cRubyHash, 0);

    va_list ar;
    va_start(ar, argc);
    for (int i = 0; i < argc; i += 2) {
	VALUE key = va_arg(ar, VALUE);
	VALUE val = va_arg(ar, VALUE);
	rhash_aset(hash, 0, key, val);
    }
    va_end(ar);

    return hash;
}

struct st_table *
rb_hash_tbl(VALUE hash)
{
    if (IS_RHASH(hash)) {
	return RHASH(hash)->tbl;
    }
    rb_raise(rb_eRuntimeError,
	    "rb_hash_tbl() won't work on pure NSDictionaries");
}

static void
default_proc_arity_check(VALUE proc)
{
    int arity = rb_proc_arity(proc);
    if (rb_proc_lambda_p(proc) && arity != 2 && (arity >= 0 || arity < -3)) {
	if (arity < 0) {
	    arity = -arity - 1;
	}
	rb_raise(rb_eTypeError, "default_proc takes two arguments (2 for %d)",
		arity);
    }
}

/*
 *  call-seq:
 *     Hash.new                          => hash
 *     Hash.new(obj)                     => aHash
 *     Hash.new {|hash, key| block }     => aHash
 *
 *  Returns a new, empty hash. If this hash is subsequently accessed by
 *  a key that doesn't correspond to a hash entry, the value returned
 *  depends on the style of <code>new</code> used to create the hash. In
 *  the first form, the access returns <code>nil</code>. If
 *  <i>obj</i> is specified, this single object will be used for
 *  all <em>default values</em>. If a block is specified, it will be
 *  called with the hash object and the key, and should return the
 *  default value. It is the block's responsibility to store the value
 *  in the hash if required.
 *
 *     h = Hash.new("Go Fish")
 *     h["a"] = 100
 *     h["b"] = 200
 *     h["a"]           #=> 100
 *     h["c"]           #=> "Go Fish"
 *     # The following alters the single default object
 *     h["c"].upcase!   #=> "GO FISH"
 *     h["d"]           #=> "GO FISH"
 *     h.keys           #=> ["a", "b"]
 *
 *     # While this creates a new default object each time
 *     h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }
 *     h["c"]           #=> "Go Fish: c"
 *     h["c"].upcase!   #=> "GO FISH: C"
 *     h["d"]           #=> "Go Fish: d"
 *     h.keys           #=> ["c", "d"]
 *
 */

static VALUE
rhash_initialize(VALUE hash, SEL sel, int argc, const VALUE *argv)
{
    VALUE ifnone;

    rhash_modify(hash);
    if (rb_block_given_p()) {
	if (argc > 0) {
	    rb_raise(rb_eArgError, "wrong number of arguments");
	}
	ifnone = rb_block_proc();
	default_proc_arity_check(ifnone);
	GC_WB(&RHASH(hash)->ifnone, rb_block_proc());
	RHASH(hash)->has_proc_default = true;
    }
    else {
	rb_scan_args(argc, argv, "01", &ifnone);
	if (ifnone != Qnil) {
	    GC_WB(&RHASH(hash)->ifnone, ifnone);
	}
    }
    return hash;
}

VALUE
rb_hash_new2(int argc, const VALUE *argv)
{
    VALUE h = rhash_alloc(rb_cRubyHash, 0);
    rhash_initialize(h, 0, argc, argv);
    return h;
}

/*
 *  call-seq:
 *     Hash.try_convert(obj) -> hash or nil
 *
 *  Try to convert <i>obj</i> into a hash, using to_hash method.
 *  Returns converted hash or nil if <i>obj</i> cannot be converted
 *  for any reason.
 *
 *     Hash.try_convert({1=>2})   # => {1=>2}
 *     Hash.try_convert("1=>2")   # => nil
 */

static VALUE
rhash_try_convert(VALUE dummy, SEL sel, VALUE hash)
{
    return rb_check_convert_type(hash, T_HASH, "Hash", "to_hash");
}

/*
 *  call-seq:
 *     Hash[ [key =>|, value]* ]   => hash
 *
 *  Creates a new hash populated with the given objects. Equivalent to
 *  the literal <code>{ <i>key</i>, <i>value</i>, ... }</code>. Keys and
 *  values occur in pairs, so there must be an even number of arguments.
 *
 *     Hash["a", 100, "b", 200]       #=> {"a"=>100, "b"=>200}
 *     Hash["a" => 100, "b" => 200]   #=> {"a"=>100, "b"=>200}
 *     { "a" => 100, "b" => 200 }     #=> {"a"=>100, "b"=>200}
 */

static VALUE
rhash_create(VALUE klass, SEL sel, int argc, VALUE *argv)
{
    if (argc == 1) {
	VALUE tmp = rhash_try_convert(Qnil, 0, argv[0]);
	if (!NIL_P(tmp)) {
	    VALUE hash = rhash_alloc(klass, 0);
	    if (IS_RHASH(tmp)) {
		GC_WB(&RHASH(hash)->tbl, st_copy(RHASH(tmp)->tbl));
	    }
	    else {
		VALUE keys = rb_hash_keys(tmp);
		for (long i = 0, count = RARRAY_LEN(keys); i < count; i++) {
		    VALUE key = RARRAY_AT(keys, i);
		    VALUE val = rb_hash_lookup(tmp, key);
		    rhash_aset(hash, 0, key, val);  
		}
	    }
	    return hash;
	}

	tmp = rb_check_array_type(argv[0]);
	if (!NIL_P(tmp)) {
	    VALUE hash = rhash_alloc(klass, 0);
	    for (int i = 0; i < RARRAY_LEN(tmp); ++i) {
		VALUE v = rb_check_array_type(RARRAY_AT(tmp, i));
		if (NIL_P(v)) {
		    continue;
		}
		const long len = RARRAY_LEN(v);
		if (len < 1 || 2 < len) {
		    continue;
		}
		rhash_aset(hash, 0, RARRAY_AT(v, 0), RARRAY_AT(v, 1));
	    }
	    return hash;
	}
    }
    if (argc % 2 != 0) {
	rb_raise(rb_eArgError, "odd number of arguments for Hash");
    }

    VALUE hash = rhash_alloc(klass, 0);
    for (int i = 0; i < argc; i += 2) {
        rb_hash_aset(hash, argv[i], argv[i + 1]);
    }

    return hash;
}

static VALUE
to_hash(VALUE hash)
{
    return rb_convert_type(hash, T_HASH, "Hash", "to_hash");
}

/*
 *  call-seq:
 *     hsh.rehash -> hsh
 *
 *  Rebuilds the hash based on the current hash values for each key. If
 *  values of key objects have changed since they were inserted, this
 *  method will reindex <i>hsh</i>. If <code>Hash#rehash</code> is
 *  called while an iterator is traversing the hash, an
 *  <code>RuntimeError</code> will be raised in the iterator.
 *
 *     a = [ "a", "b" ]
 *     c = [ "c", "d" ]
 *     h = { a => 100, c => 300 }
 *     h[a]       #=> 100
 *     a[0] = "z"
 *     h[a]       #=> nil
 *     h.rehash   #=> {["z", "b"]=>100, ["c", "d"]=>300}
 *     h[a]       #=> 100
 */

static int
rhash_rehash_i(VALUE key, VALUE value, VALUE arg)
{
    st_table *tbl = (st_table *)arg;
    if (key != Qundef) {
	st_insert(tbl, key, value);
    }
    return ST_CONTINUE;
}

static VALUE
rhash_rehash(VALUE hash, SEL sel)
{
    rhash_modify(hash);
    st_table *tbl = st_init_table_with_size(RHASH(hash)->tbl->type,
	    RHASH(hash)->tbl->num_entries);
    rb_hash_foreach(hash, rhash_rehash_i, (VALUE)tbl);
    //st_free_table(RHASH(hash)->tbl);
    GC_WB(&RHASH(hash)->tbl, tbl);
    return hash;
}

/*
 *  call-seq:
 *     hsh[key]    =>  value
 *
 *  Element Reference---Retrieves the <i>value</i> object corresponding
 *  to the <i>key</i> object. If not found, returns the a default value (see
 *  <code>Hash::new</code> for details).
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h["a"]   #=> 100
 *     h["c"]   #=> nil
 *
 */

static inline VALUE
rhash_call_default(VALUE hash, VALUE key)
{
    return rb_vm_call(hash, selDefault, 1, &key);
}

VALUE
rhash_aref(VALUE hash, SEL sel, VALUE key)
{
    VALUE val = rhash_lookup(hash, key);
    if (val == Qundef) {
	if (*(VALUE *)hash == rb_cRubyHash
		&& RHASH(hash)->ifnone == Qnil) {
	    return Qnil;
	}
	return rhash_call_default(hash, key);
    }
    return val;
}

/*
 *  call-seq:
 *     hsh.fetch(key [, default] )       => obj
 *     hsh.fetch(key) {| key | block }   => obj
 *
 *  Returns a value from the hash for the given key. If the key can't be
 *  found, there are several options: With no other arguments, it will
 *  raise an <code>KeyError</code> exception; if <i>default</i> is
 *  given, then that will be returned; if the optional code block is
 *  specified, then that will be run and its result returned.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.fetch("a")                            #=> 100
 *     h.fetch("z", "go fish")                 #=> "go fish"
 *     h.fetch("z") { |el| "go fish, #{el}"}   #=> "go fish, z"
 *
 *  The following example shows that an exception is raised if the key
 *  is not found and a default value is not supplied.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.fetch("z")
 *
 *  <em>produces:</em>
 *
 *     prog.rb:2:in `fetch': key not found (KeyError)
 *      from prog.rb:2
 *
 */

static VALUE
rhash_fetch(VALUE hash, SEL sel, int argc, VALUE *argv)
{
    VALUE key, if_none;
    rb_scan_args(argc, argv, "11", &key, &if_none);

    const bool block_given = rb_block_given_p();
    if (block_given && argc == 2) {
	rb_warn("block supersedes default value argument");
    }

    VALUE v = rhash_lookup(hash, key);
    if (v != Qundef) {
	return v;
    }
    if (block_given) {
	return rb_yield(key);
    }
    if (argc == 1) {
	rb_raise(rb_eKeyError, "key not found");
    }
    return if_none;
}

/*
 *  call-seq:
 *     hsh.default(key=nil)   => obj
 *
 *  Returns the default value, the value that would be returned by
 *  <i>hsh</i>[<i>key</i>] if <i>key</i> did not exist in <i>hsh</i>.
 *  See also <code>Hash::new</code> and <code>Hash#default=</code>.
 *
 *     h = Hash.new                            #=> {}
 *     h.default                               #=> nil
 *     h.default(2)                            #=> nil
 *
 *     h = Hash.new("cat")                     #=> {}
 *     h.default                               #=> "cat"
 *     h.default(2)                            #=> "cat"
 *
 *     h = Hash.new {|h,k| h[k] = k.to_i*10}   #=> {}
 *     h.default                               #=> nil
 *     h.default(2)                            #=> 20
 */

static VALUE
rhash_default(VALUE hash, SEL sel, int argc, VALUE *argv)
{
    VALUE key;
    rb_scan_args(argc, argv, "01", &key);

    if (RHASH(hash)->has_proc_default) {
	if (argc == 0) {
	    return Qnil;
	}
	return rb_funcall(RHASH(hash)->ifnone, id_yield, 2, hash, key);
    }
    return RHASH(hash)->ifnone;
}

/*
 *  call-seq:
 *     hsh.default = obj     => hsh
 *
 *  Sets the default value, the value returned for a key that does not
 *  exist in the hash. It is not possible to set the a default to a
 *  <code>Proc</code> that will be executed on each key lookup.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.default = "Go fish"
 *     h["a"]     #=> 100
 *     h["z"]     #=> "Go fish"
 *     # This doesn't do what you might hope...
 *     h.default = proc do |hash, key|
 *       hash[key] = key + key
 *     end
 *     h[2]       #=> #<Proc:0x401b3948@-:6>
 *     h["cat"]   #=> #<Proc:0x401b3948@-:6>
 */

VALUE
rhash_set_default(VALUE hash, SEL sel, VALUE ifnone)
{
    rhash_modify(hash);
    GC_WB(&RHASH(hash)->ifnone, ifnone);
    RHASH(hash)->has_proc_default = false;
    return ifnone;
}

/*
 *  call-seq:
 *     hsh.default_proc -> anObject
 *
 *  If <code>Hash::new</code> was invoked with a block, return that
 *  block, otherwise return <code>nil</code>.
 *
 *     h = Hash.new {|h,k| h[k] = k*k }   #=> {}
 *     p = h.default_proc                 #=> #<Proc:0x401b3d08@-:1>
 *     a = []                             #=> []
 *     p.call(a, 2)
 *     a                                  #=> [nil, nil, 4]
 */

static VALUE
rhash_default_proc(VALUE hash, SEL sel)
{
    return RHASH(hash)->has_proc_default ? RHASH(hash)->ifnone : Qnil;
}

/*
 *  call-seq:
 *     hsh.default_proc = proc_obj     => proc_obj
 *
 *  Sets the default proc to be executed on each key lookup.
 *
 *     h.default_proc = proc do |hash, key|
 *       hash[key] = key + key
 *     end
 *     h[2]       #=> 4
 *     h["cat"]   #=> "catcat"
 */

static VALUE
rhash_set_default_proc(VALUE hash, SEL sel, VALUE proc)
{
    rhash_modify(hash);
    VALUE tmp = rb_check_convert_type(proc, T_DATA, "Proc", "to_proc");
    if (NIL_P(tmp)) {
        rb_raise(rb_eTypeError,
		"wrong default_proc type %s (expected Proc)",
		rb_obj_classname(proc));
    }
    proc = tmp;
    default_proc_arity_check(proc);
    GC_WB(&RHASH(hash)->ifnone, proc);
    RHASH(hash)->has_proc_default = true;
    return proc;
}

/*
 *  call-seq:
 *     hsh.key(value)    => key
 *
 *  Returns the key for a given value. If not found, returns <code>nil</code>.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.key(200)   #=> "b"
 *     h.key(999)   #=> nil
 *
 */

static int
key_i(VALUE key, VALUE value, VALUE *args)
{
    if (rb_equal(value, args[0])) {
	args[1] = key;
	return ST_STOP;
    }
    return ST_CONTINUE;
}

static VALUE
rhash_key(VALUE hash, SEL sel, VALUE value)
{
    VALUE args[2] = {value, Qnil};
    rhash_foreach(hash, key_i, (st_data_t)args);
    return args[1];
}

/* :nodoc: */
static VALUE
rhash_index(VALUE hash, SEL sel, VALUE value)
{
    rb_warn("Hash#index is deprecated; use Hash#key");
    return rhash_key(hash, 0, value);
}

/*
 *  call-seq:
 *     hsh.delete(key)                   => value
 *     hsh.delete(key) {| key | block }  => value
 *
 *  Deletes and returns the value from <i>hsh</i> whose key is
 *  equal to <i>key</i>. If the key is not found, returns nil.
 *  If the optional code block is given and the
 *  key is not found, pass in the key and return the result of
 *  <i>block</i>.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.delete("a")                              #=> 100
 *     h.delete("z")                              #=> nil
 *     h.delete("z") { |el| "#{el} not found" }   #=> "z not found"
 *
 */

static VALUE
rhash_delete(VALUE hash, SEL sel, VALUE key)
{
    rhash_modify(hash);
    VALUE val = rhash_delete_key(hash, key);
    if (val != Qundef) {
	return val;
    }
    if (rb_block_given_p()) {
	return rb_yield(key);
    }
    return Qnil;
}

/*
 *  call-seq:
 *     hsh.shift -> anArray or obj
 *
 *  Removes a key-value pair from <i>hsh</i> and returns it as the
 *  two-item array <code>[</code> <i>key, value</i> <code>]</code>, or
 *  the hash's default value if the hash is empty.
 *
 *     h = { 1 => "a", 2 => "b", 3 => "c" }
 *     h.shift   #=> [1, "a"]
 *     h         #=> {2=>"b", 3=>"c"}
 */

static int
shift_i(VALUE key, VALUE value, VALUE arg)
{
    VALUE *ret = (VALUE *)arg;
    if (key != Qundef) {
	ret[0] = key;
	ret[1] = value;
	return ST_STOP;
    }
    return ST_CONTINUE;
}

static VALUE
rhash_shift(VALUE hash, SEL sel)
{
    VALUE args[2] = {0, 0};
    rhash_modify(hash);
    rhash_foreach(hash, shift_i, (st_data_t)args);
    if (args[0] != 0 && args[1] != 0) {
	rhash_delete_key(hash, args[0]);
	return rb_assoc_new(args[0], args[1]);
    }

    if (RHASH(hash)->ifnone != Qnil) {
	if (RHASH(hash)->has_proc_default) {
	    return rb_funcall(RHASH(hash)->ifnone, id_yield, 2, hash,
		    Qnil);
	}
	return RHASH(hash)->ifnone;
    }
    return Qnil;
}

/*
 *  call-seq:
 *     hsh.delete_if {| key, value | block }  -> hsh
 *
 *  Deletes every key-value pair from <i>hsh</i> for which <i>block</i>
 *  evaluates to <code>true</code>.
 *
 *     h = { "a" => 100, "b" => 200, "c" => 300 }
 *     h.delete_if {|key, value| key >= "b" }   #=> {"a"=>100}
 *
 */

static int
delete_if_i(VALUE key, VALUE value, VALUE ary)
{
    if (key != Qundef) {
	const bool ok = RTEST(rb_yield_values(2, key, value));
	ST_STOP_IF_BROKEN();
	if (ok) {
	    rb_ary_push(ary, key);
	}
    }
    return ST_CONTINUE;
}

static VALUE
rhash_delete_if(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rhash_modify(hash);
    VALUE ary = rb_ary_new();
    rhash_foreach(hash, delete_if_i, ary);
    RETURN_IF_BROKEN();
    for (int i = 0, count = RARRAY_LEN(ary); i < count; i++) {
	VALUE key = RARRAY_AT(ary, i);
	rhash_delete_key(hash, key);	
    }
    return hash;
}

VALUE
rb_hash_delete_if(VALUE hash)
{
    return rhash_delete_if(hash, 0);
}

/*
 *  call-seq:
 *     hsh.reject! {| key, value | block }  -> hsh or nil
 *
 *  Equivalent to <code>Hash#delete_if</code>, but returns
 *  <code>nil</code> if no changes were made.
 */

static VALUE
rhash_reject_bang(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    const long n = rhash_len(hash);
    rhash_delete_if(hash, 0);
    return n == rhash_len(hash) ? Qnil : hash;
}

/*
 *  call-seq:
 *     hsh.reject {| key, value | block }  -> a_hash
 *
 *  Same as <code>Hash#delete_if</code>, but works on (and returns) a
 *  copy of the <i>hsh</i>. Equivalent to
 *  <code><i>hsh</i>.dup.delete_if</code>.
 *
 */

static VALUE
rhash_reject(VALUE hash, SEL sel)
{
    return rhash_delete_if(rhash_dup(hash, 0), 0);
}

/*
 * call-seq:
 *   hsh.values_at(key, ...)   => array
 *
 * Return an array containing the values associated with the given keys.
 * Also see <code>Hash.select</code>.
 *
 *   h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
 *   h.values_at("cow", "cat")  #=> ["bovine", "feline"]
 */

static VALUE
rhash_values_at(VALUE hash, SEL sel, int argc, VALUE *argv)
{
    VALUE result = rb_ary_new2(argc);
    for (int i = 0; i < argc; i++) {
	rb_ary_push(result, rhash_aref(hash, 0, argv[i]));
    }
    return result;
}

/*
 *  call-seq:
 *     hsh.select {|key, value| block}   => a_hash
 *
 *  Returns a new hash consisting of entries which the block returns true.
 *
 *     h = { "a" => 100, "b" => 200, "c" => 300 }
 *     h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
 *     h.select {|k,v| v < 200}  #=> {"a" => 100}
 */

static int
select_i(VALUE key, VALUE value, VALUE result)
{
    if (key != Qundef) {
	const bool ok = RTEST(rb_yield_values(2, key, value));
	ST_STOP_IF_BROKEN();
	if (ok) {
	    rb_hash_aset(result, key, value);
	}
    }
    return ST_CONTINUE;
}

static VALUE
rhash_select(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    VALUE result = rb_hash_new();
    rhash_foreach(hash, select_i, result);
    RETURN_IF_BROKEN();
    return result;
}

/*
 *  call-seq:
 *     hsh.select! {| key, value | block }  -> hsh or nil
 *     hsh.select!                          -> an_enumerator
 *
 *  Equivalent to <code>Hash#keep_if</code>, but returns
 *  <code>nil</code> if no changes were made.
 */

static int
keep_if_i(VALUE key, VALUE value, VALUE hash)
{
    if (key != Qundef) {
	const bool ok = RTEST(rb_yield_values(2, key, value));
	ST_STOP_IF_BROKEN();
	if (!ok) {
	    return ST_DELETE;
	}
    }
    return ST_CONTINUE;
}

static VALUE
rhash_select_bang(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rhash_modify(hash);
    const long n = rhash_len(hash);
    rb_hash_foreach(hash, keep_if_i, hash);
    RETURN_IF_BROKEN();
    return n == rhash_len(hash) ? Qnil : hash;
}

/*
 *  call-seq:
 *     hsh.keep_if {| key, value | block }  -> hsh
 *     hsh.keep_if                          -> an_enumerator
 *
 *  Deletes every key-value pair from <i>hsh</i> for which <i>block</i>
 *  evaluates to false.
 *
 *  If no block is given, an enumerator is returned instead.
 *
 */

VALUE
rhash_keep_if(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rhash_modify(hash);
    rhash_foreach(hash, keep_if_i, hash);
    return hash;
}

/*
 *  call-seq:
 *     hsh.clear -> hsh
 *
 *  Removes all key-value pairs from <i>hsh</i>.
 *
 *     h = { "a" => 100, "b" => 200 }   #=> {"a"=>100, "b"=>200}
 *     h.clear                          #=> {}
 *
 */

static VALUE
rhash_clear(VALUE hash, SEL sel)
{
    rhash_modify(hash);
    st_clear(RHASH(hash)->tbl);
    return hash;
}

/*
 *  call-seq:
 *     hsh[key] = value        => value
 *     hsh.store(key, value)   => value
 *
 *  Element Assignment---Associates the value given by
 *  <i>value</i> with the key given by <i>key</i>.
 *  <i>key</i> should not have its value changed while it is in
 *  use as a key (a <code>String</code> passed as a key will be
 *  duplicated and frozen).
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h["a"] = 9
 *     h["c"] = 4
 *     h   #=> {"a"=>9, "b"=>200, "c"=>4}
 *
 */

VALUE
rhash_aset(VALUE hash, SEL sel, VALUE key, VALUE val)
{
    rhash_modify(hash);
    if (TYPE(key) == T_STRING && !OBJ_FROZEN(key)) {
        key = rb_str_dup(key);
        OBJ_FREEZE(key);
    }
    st_insert(RHASH(hash)->tbl, key, val);
    return val;
}

static int
replace_i(VALUE key, VALUE val, VALUE hash)
{
    if (key != Qundef) {
	rb_hash_aset(hash, key, val);
    }
    return ST_CONTINUE;
}

/*
 *  call-seq:
 *     hsh.replace(other_hash) -> hsh
 *
 *  Replaces the contents of <i>hsh</i> with the contents of
 *  <i>other_hash</i>.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}
 *
 */

static VALUE
rhash_replace(VALUE hash, SEL sel, VALUE hash2)
{
    rhash_modify(hash);
    hash2 = to_hash(hash2);
    if (hash == hash2) {
	return hash;
    }

    // Copy RubyHash properties.
    if (IS_RHASH(hash2)) {
	if (RHASH(hash2)->tbl->type == &identhash) {
	    RHASH(hash)->tbl->type = &identhash;
	}
	GC_WB(&RHASH(hash)->ifnone, RHASH(hash2)->ifnone);
	RHASH(hash)->has_proc_default = RHASH(hash2)->has_proc_default;
    }

    rhash_clear(hash, 0);
    rb_hash_foreach(hash2, replace_i, hash);
    return hash;
}

/*
 *  call-seq:
 *     hsh.length    =>  fixnum
 *     hsh.size      =>  fixnum
 *
 *  Returns the number of key-value pairs in the hash.
 *
 *     h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
 *     h.length        #=> 4
 *     h.delete("a")   #=> 200
 *     h.length        #=> 3
 */

static VALUE
rhash_size(VALUE hash, SEL sel)
{
    return LONG2NUM(rhash_len(hash));
}

/*
 *  call-seq:
 *     hsh.empty?    => true or false
 *
 *  Returns <code>true</code> if <i>hsh</i> contains no key-value pairs.
 *
 *     {}.empty?   #=> true
 *
 */

static VALUE
rhash_empty(VALUE hash, SEL sel)
{
    return rhash_len(hash) == 0 ? Qtrue : Qfalse;
}

/*
 *  call-seq:
 *     hsh.each_value {| value | block } -> hsh
 *
 *  Calls <i>block</i> once for each key in <i>hsh</i>, passing the
 *  value as a parameter.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.each_value {|value| puts value }
 *
 *  <em>produces:</em>
 *
 *     100
 *     200
 */

static int
each_value_i(VALUE key, VALUE value)
{
    if (key != Qundef) {
	rb_yield(value);
	ST_STOP_IF_BROKEN();
    }
    return ST_CONTINUE;
}

static VALUE
rhash_each_value(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rhash_foreach(hash, each_value_i, 0);
    RETURN_IF_BROKEN();
    return hash;
}

/*
 *  call-seq:
 *     hsh.each_key {| key | block } -> hsh
 *
 *  Calls <i>block</i> once for each key in <i>hsh</i>, passing the key
 *  as a parameter.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.each_key {|key| puts key }
 *
 *  <em>produces:</em>
 *
 *     a
 *     b
 */

static int
each_key_i(VALUE key, VALUE value)
{
    if (key != Qundef) {
	rb_yield(key);
	ST_STOP_IF_BROKEN();
    }
    return ST_CONTINUE;
}

static VALUE
rhash_each_key(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rhash_foreach(hash, each_key_i, 0);
    RETURN_IF_BROKEN();
    return hash;
}

/*
 *  call-seq:
 *     hsh.each {| key, value | block } -> hsh
 *     hsh.each_pair {| key, value | block } -> hsh
 *
 *  Calls <i>block</i> once for each key in <i>hsh</i>, passing the key-value
 *  pair as parameters.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.each {|key, value| puts "#{key} is #{value}" }
 *
 *  <em>produces:</em>
 *
 *     a is 100
 *     b is 200
 *
 */

static int
each_pair_i(VALUE key, VALUE value)
{
    if (key != Qundef) {
	rb_yield(rb_assoc_new(key, value));
	ST_STOP_IF_BROKEN();
    }
    return ST_CONTINUE;
}

static VALUE
rhash_each_pair(VALUE hash, SEL sel)
{
    RETURN_ENUMERATOR(hash, 0, 0);
    rhash_foreach(hash, each_pair_i, 0);
    RETURN_IF_BROKEN();
    return hash;
}

/*
 *  call-seq:
 *     hsh.to_a -> array
 *
 *  Converts <i>hsh</i> to a nested array of <code>[</code> <i>key,
 *  value</i> <code>]</code> arrays.
 *
 *     h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
 *     h.to_a   #=> [["c", 300], ["a", 100], ["d", 400]]
 */

static int
to_a_i(VALUE key, VALUE value, VALUE ary)
{
    if (key != Qundef) {
	rb_ary_push(ary, rb_assoc_new(key, value));
    }
    return ST_CONTINUE;
}

static VALUE
rhash_to_a(VALUE hash, SEL sel)
{
    VALUE ary = rb_ary_new();
    rhash_foreach(hash, to_a_i, ary);
    OBJ_INFECT(ary, hash);
    return ary;
}

/*
 * call-seq:
 *   hsh.to_s   => string
 *   hsh.inspect  => string
 *
 * Return the contents of this hash as a string.
 *
 *     h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
 *     h.to_s   #=> "{\"c\"=>300, \"a\"=>100, \"d\"=>400}"
 */

static int
inspect_i(VALUE key, VALUE value, VALUE str)
{
    if (key != Qundef) {
	if (RSTRING_LEN(str) > 1) {
	    rb_str_cat2(str, ", ");
	}
	VALUE str2 = rb_inspect(key);
	rb_str_buf_append(str, str2);
	rb_str_buf_cat2(str, "=>");
	str2 = rb_inspect(value);
	rb_str_buf_append(str, str2);
    }
    return ST_CONTINUE;
}

static VALUE
inspect_hash(VALUE hash, VALUE dummy, int recur)
{
    if (recur) {
	return rb_usascii_str_new2("{...}");
    }
    VALUE str = rb_str_buf_new2("{");
    rhash_foreach(hash, inspect_i, str);
    rb_str_buf_cat2(str, "}");
    OBJ_INFECT(str, hash);
    return str;
}

static VALUE
rhash_inspect(VALUE hash, SEL sel)
{
    if (RHASH_EMPTY_P(hash)) {
	return rb_usascii_str_new2("{}");
    }
    return rb_exec_recursive(inspect_hash, hash, 0);
}

/*
 * call-seq:
 *    hsh.to_hash   => hsh
 *
 * Returns <i>self</i>.
 */

static VALUE
rhash_to_hash(VALUE hash, SEL sel)
{
    return hash;
}

/*
 *  call-seq:
 *     hsh.keys    => array
 *
 *  Returns a new array populated with the keys from this hash. See also
 *  <code>Hash#values</code>.
 *
 *     h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }
 *     h.keys   #=> ["a", "b", "c", "d"]
 *
 */

static int
keys_i(VALUE key, VALUE value, VALUE ary)
{
    if (key != Qundef) {
	rb_ary_push(ary, key);
    }
    return ST_CONTINUE;
}

VALUE
rhash_keys(VALUE hash, SEL sel)
{
    VALUE ary = rb_ary_new();
    rhash_foreach(hash, keys_i, ary);
    return ary;
}

/*
 *  call-seq:
 *     hsh.values    => array
 *
 *  Returns a new array populated with the values from <i>hsh</i>. See
 *  also <code>Hash#keys</code>.
 *
 *     h = { "a" => 100, "b" => 200, "c" => 300 }
 *     h.values   #=> [100, 200, 300]
 *
 */

static int
values_i(VALUE key, VALUE value, VALUE ary)
{
    if (key != Qundef) {
	rb_ary_push(ary, value);
    }
    return ST_CONTINUE;
}

static VALUE
rhash_values(VALUE hash, SEL sel)
{
    VALUE ary = rb_ary_new();
    rhash_foreach(hash, values_i, ary);
    return ary;
}

/*
 *  call-seq:
 *     hsh.has_key?(key)    => true or false
 *     hsh.include?(key)    => true or false
 *     hsh.key?(key)        => true or false
 *     hsh.member?(key)     => true or false
 *
 *  Returns <code>true</code> if the given key is present in <i>hsh</i>.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.has_key?("a")   #=> true
 *     h.has_key?("z")   #=> false
 *
 */

VALUE
rhash_has_key(VALUE hash, SEL sel, VALUE key)
{
    return st_lookup(RHASH(hash)->tbl, key, 0) ? Qtrue : Qfalse;
}

/*
 *  call-seq:
 *     hsh.has_value?(value)    => true or false
 *     hsh.value?(value)        => true or false
 *
 *  Returns <code>true</code> if the given value is present for some key
 *  in <i>hsh</i>.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.has_value?(100)   #=> true
 *     h.has_value?(999)   #=> false
 */

static int
search_value(VALUE key, VALUE value, VALUE arg)
{
    VALUE *data = (VALUE *)arg;
    if (key != Qundef) {
	if (rb_equal(value, data[1])) {
	    data[0] = Qtrue;
	    return ST_STOP;
	}
    }
    return ST_CONTINUE;
}

static VALUE
rhash_has_value(VALUE hash, SEL sel, VALUE val)
{
    VALUE data[2] = {Qfalse, val};
    rhash_foreach(hash, search_value, (VALUE)data);
    return data[0];
}

/*
 *  call-seq:
 *     hsh == other_hash    => true or false
 *
 *  Equality---Two hashes are equal if they each contain the same number
 *  of keys and if each key-value pair is equal to (according to
 *  <code>Object#==</code>) the corresponding elements in the other
 *  hash.
 *
 *     h1 = { "a" => 1, "c" => 2 }
 *     h2 = { 7 => 35, "c" => 2, "a" => 1 }
 *     h3 = { "a" => 1, "c" => 2, 7 => 35 }
 *     h4 = { "a" => 1, "d" => 2, "f" => 35 }
 *     h1 == h2   #=> false
 *     h2 == h3   #=> true
 *     h3 == h4   #=> false
 *
 */

struct equal_data {
    VALUE result;
    st_table *tbl;
    bool eql;
};

static int
eql_i(VALUE key, VALUE val1, VALUE arg)
{
    struct equal_data *data = (struct equal_data *)arg;
    VALUE val2;

    if (key == Qundef) {
	return ST_CONTINUE;
    }
    if (!st_lookup(data->tbl, key, &val2)) {
        data->result = Qfalse;
        return ST_STOP;
    }
    if (data->eql) {
	if (!rb_eql(val1, val2)) {
	    data->result = Qfalse;
	    return ST_STOP;
	}
    }
    else {
	if (rb_equal(val1, val2) != Qtrue) {
	    data->result = Qfalse;
	    return ST_STOP;
	}
    }
    return ST_CONTINUE;
}

static VALUE
recursive_eql(VALUE hash1, VALUE data, int recur)
{
    if (recur) {
	return Qtrue;
    }
    ((struct equal_data *)data)->result = Qtrue;
    rb_hash_foreach(hash1, eql_i, data);
    return ((struct equal_data *)data)->result; 
}

static VALUE
hash_equal(VALUE hash1, VALUE hash2, bool eql)
{
    if (hash1 == hash2) {
	return Qtrue;
    }
    if (TYPE(hash2) != T_HASH) {
	if (!rb_respond_to(hash2, rb_intern("to_hash"))) {
	    return Qfalse;
	}
	if (eql) {
	    return rb_eql(hash2, hash1);
	}
	else {
	    return rb_equal(hash2, hash1);
	}
    }
    if (RHASH_SIZE(hash1) != RHASH_SIZE(hash2)) {
	return Qfalse;
    }
    if (IS_RHASH(hash2)) {
	struct equal_data data;
	data.tbl = RHASH(hash2)->tbl;
	data.eql = eql;
	return rb_exec_recursive(recursive_eql, hash1, (VALUE)&data);
    }
    else {
	return CFEqual((CFTypeRef)hash1, (CFTypeRef)hash2) ? Qtrue : Qfalse;
    }
}

static VALUE
rhash_equal(VALUE hash1, SEL sel, VALUE hash2)
{
    return hash_equal(hash1, hash2, false);
}

VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, false);
}

/*
 *  call-seq:
 *     hash.eql?(other)  -> true or false
 *
 *  Returns <code>true</code> if <i>hash</i> and <i>other</i> are
 *  both hashes with the same content.
 */

static VALUE
rhash_eql(VALUE hash1, SEL sel, VALUE hash2)
{
    return hash_equal(hash1, hash2, true);
}

/*
 *  call-seq:
 *     hsh.invert -> aHash
 *
 *  Returns a new hash created by using <i>hsh</i>'s values as keys, and
 *  the keys as values.
 *
 *     h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
 *     h.invert   #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}
 *
 */

static int
invert_i(VALUE key, VALUE value, VALUE hash)
{
    if (key != Qundef) {
	rhash_aset(hash, 0, value, key);
    }
    return ST_CONTINUE;
}

static VALUE
rhash_invert(VALUE hash, SEL sel)
{
    VALUE h = rb_hash_new();
    rhash_foreach(hash, invert_i, h);
    return h;
}

/*
 *  call-seq:
 *     hsh.merge!(other_hash)                                 => hsh
 *     hsh.update(other_hash)                                 => hsh
 *     hsh.merge!(other_hash){|key, oldval, newval| block}    => hsh
 *     hsh.update(other_hash){|key, oldval, newval| block}    => hsh
 *
 *  Adds the contents of <i>other_hash</i> to <i>hsh</i>.  If no
 *  block is specified entries with duplicate keys are overwritten
 *  with the values from <i>other_hash</i>, otherwise the value
 *  of each duplicate key is determined by calling the block with
 *  the key, its value in <i>hsh</i> and its value in <i>other_hash</i>.
 *
 *     h1 = { "a" => 100, "b" => 200 }
 *     h2 = { "b" => 254, "c" => 300 }
 *     h1.merge!(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}
 *
 *     h1 = { "a" => 100, "b" => 200 }
 *     h2 = { "b" => 254, "c" => 300 }
 *     h1.merge!(h2) { |key, v1, v2| v1 }
 *                     #=> {"a"=>100, "b"=>200, "c"=>300}
 */

static int
update_i(VALUE key, VALUE value, VALUE hash)
{
    if (key != Qundef) {
	rhash_aset(hash, 0, key, value);
    }
    return ST_CONTINUE;
}

static int
update_block_i(VALUE key, VALUE value, VALUE hash)
{
    if (key != Qundef) {
	if (rhash_has_key(hash, 0, key)) {
	    value = rb_yield_values(3, key, rhash_aref(hash, 0, key), value);
	    ST_STOP_IF_BROKEN();
	}
	rhash_aset(hash, 0, key, value);
    }
    return ST_CONTINUE;
}

static VALUE
rhash_update(VALUE hash1, SEL sel, VALUE hash2)
{
    rhash_modify(hash1);
    hash2 = to_hash(hash2);
    if (rb_block_given_p()) {
	rb_hash_foreach(hash2, update_block_i, hash1);
	RETURN_IF_BROKEN();
    }
    else {
	rb_hash_foreach(hash2, update_i, hash1);
    }
    return hash1;
}

/*
 *  call-seq:
 *     hsh.merge(other_hash)                              -> a_hash
 *     hsh.merge(other_hash){|key, oldval, newval| block} -> a_hash
 *
 *  Returns a new hash containing the contents of <i>other_hash</i> and
 *  the contents of <i>hsh</i>, overwriting entries in <i>hsh</i> with
 *  duplicate keys with those from <i>other_hash</i>.
 *
 *     h1 = { "a" => 100, "b" => 200 }
 *     h2 = { "b" => 254, "c" => 300 }
 *     h1.merge(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}
 *     h1             #=> {"a"=>100, "b"=>200}
 *
 */

static VALUE
rhash_merge(VALUE hash1, SEL sel, VALUE hash2)
{
    return rhash_update(rhash_dup(hash1, 0), 0, hash2);
}

/*
 *  call-seq:
 *     hash.assoc(obj)   ->  an_array  or  nil
 *
 *  Searches through the hash comparing _obj_ with the key using <code>==</code>.
 *  Returns the key-value pair (two elements array) or +nil+
 *  if no match is found.  See <code>Array#assoc</code>.
 *
 *     h = {"colors"  => ["red", "blue", "green"],
 *          "letters" => ["a", "b", "c" ]}
 *     h.assoc("letters")  #=> ["letters", ["a", "b", "c"]]
 *     h.assoc("foo")      #=> nil
 */

static int
assoc_i(VALUE key, VALUE val, VALUE *args)
{
    if (key != Qundef) {
	if (RTEST(rb_equal(args[0], key))) {
	    args[1] = rb_assoc_new(key, val);
	    return ST_STOP;
	}
    }
    return ST_CONTINUE;
}

static VALUE
rhash_assoc(VALUE hash, SEL sel, VALUE obj)
{
    VALUE args[2] = {obj, Qnil};
    rhash_foreach(hash, assoc_i, (st_data_t)args);
    return args[1];
}

/*
 *  call-seq:
 *     hash.rassoc(key) -> an_array or nil
 *
 *  Searches through the hash comparing _obj_ with the value using <code>==</code>.
 *  Returns the first key-value pair (two elements array) that matches. See
 *  also <code>Array#rassoc</code>.
 *
 *     a = {1=> "one", 2 => "two", 3 => "three", "ii" => "two"}
 *     a.rassoc("two")    #=> [2, "two"]
 *     a.rassoc("four")   #=> nil
 */

static int
rassoc_i(VALUE key, VALUE val, VALUE *args)
{
    if (key != Qundef) {
	if (RTEST(rb_equal(args[0], val))) {
	    args[1] = rb_assoc_new(key, val);
	    return ST_STOP;
	}
    }
    return ST_CONTINUE;
}

VALUE
rhash_rassoc(VALUE hash, SEL sel, VALUE obj)
{
    VALUE args[2] = {obj, Qnil};
    rhash_foreach(hash, rassoc_i, (st_data_t)args);
    return args[1];
}

/*
 *  call-seq:
 *     hash.flatten -> an_array
 *     hash.flatten(level) -> an_array
 *
 *  Returns a new array that is a one-dimensional flattening of this
 *  hash. That is, for every key or value that is an array, extract
 *  its elements into the new array.  Unlike Array#flatten, this
 *  method does not flatten recursively by default.  If the optional
 *  <i>level</i> argument determines the level of recursion to flatten.
 *
 *     a =  {1=> "one", 2 => [2,"two"], 3 => "three"}
 *     a.flatten    # => [1, "one", 2, [2, "two"], 3, "three"]
 *     a.flatten(2) # => [1, "one", 2, 2, "two", 3, "three"]
 */

static VALUE
rhash_flatten(VALUE hash, SEL sel, int argc, VALUE *argv)
{
    VALUE tmp, ary = rhash_to_a(hash, 0);
    if (argc == 0) {
	argc = 1;
	tmp = INT2FIX(1);
	argv = &tmp;
    }
    rb_vm_call(ary, selFlattenBang, argc, argv);
    return ary;
}

/*
 *  call-seq:
 *     hsh.compare_by_identity => hsh
 *
 *  Makes <i>hsh</i> to compare its keys by their identity, i.e. it
 *  will consider exact same objects as same keys.
 *
 *     h1 = { "a" => 100, "b" => 200, :c => "c" }
 *     h1["a"]        #=> 100
 *     h1.compare_by_identity
 *     h1.compare_by_identity? #=> true
 *     h1["a"]        #=> nil  # different objects.
 *     h1[:c]         #=> "c"  # same symbols are all same.
 *
 */

static VALUE
rhash_compare_by_id(VALUE hash, SEL sel)
{
    rhash_modify(hash);
    RHASH(hash)->tbl->type = &identhash;
    rhash_rehash(hash, 0);
    return hash;
}

/*
 *  call-seq:
 *     hsh.compare_by_identity? => true or false
 *
 *  Returns <code>true</code> if <i>hsh</i> will compare its keys by
 *  their identity.  Also see <code>Hash#compare_by_identity</code>.
 *
 */

static VALUE
rhash_compare_by_id_p(VALUE hash, SEL sel)
{
    return RHASH(hash)->tbl->type == &identhash ? Qtrue : Qfalse;
}

bool
rb_objc_hash_is_pure(VALUE hash)
{
    VALUE k = *(VALUE *)hash;
    while (RCLASS_SINGLETON(k)) {
        k = RCLASS_SUPER(k);
    }
    if (k == rb_cRubyHash) {
	return true;
    }
    while (k != 0) {
	if (k == rb_cRubyHash) {
	    return false;
	}
	k = RCLASS_SUPER(k);
    }
    return true;
}

static VALUE rb_cRubyHashKeyEnumerator;

typedef struct {
    VALUE klass;
    VALUE hash;
    VALUE keys;
    unsigned pos;
} rb_hash_keyenum_t;

static void *
imp_rhash_keyenum_allObjects(void *rcv, SEL sel)
{
    rb_hash_keyenum_t *ke = (rb_hash_keyenum_t *)rcv;
    return (void *)ke->keys;
}

static void *
imp_rhash_keyenum_nextObject(void *rcv, SEL sel)
{
    rb_hash_keyenum_t *ke = (rb_hash_keyenum_t *)rcv;
    if (ke->pos == RARRAY_LEN(ke->keys)) {
	return NULL;
    }
    VALUE key = RARRAY_AT(ke->keys, ke->pos);
    ke->pos++;
    return (void *)RB2OC(key);
}

static CFIndex
imp_rhash_count(void *rcv, SEL sel)
{
    return RHASH(rcv)->tbl->num_entries;
}

static void *
imp_rhash_objectForKey(void *rcv, SEL sel, void *key)
{
    VALUE val;
    if (!st_lookup(RHASH(rcv)->tbl, OC2RB(key), &val)) {
	return NULL;
    }
    return RB2OC(val);
}

static void *
imp_rhash_keyEnumerator(void *rcv, SEL sel)
{
    NEWOBJ(keyenum, rb_hash_keyenum_t);
    keyenum->klass = rb_cRubyHashKeyEnumerator;
    GC_WB(&keyenum->hash, rcv);
    VALUE ary = rb_ary_new();
    st_foreach_safe(RHASH(rcv)->tbl, keys_i, (st_data_t)ary);
    GC_WB(&keyenum->keys, ary); 
    keyenum->pos = 0;
    return keyenum;
}

static void
imp_rhash_setObjectForKey(void *rcv, SEL sel, void *val, void *key)
{
    st_insert(RHASH(rcv)->tbl, OC2RB(key), OC2RB(val));
}

static void
imp_rhash_removeObjectForKey(void *rcv, SEL sel, void *key)
{
    VALUE rkey = OC2RB(key);
    st_delete(RHASH(rcv)->tbl, &rkey, NULL);
}

/*
 *  A <code>Hash</code> is a collection of key-value pairs. It is
 *  similar to an <code>Array</code>, except that indexing is done via
 *  arbitrary keys of any object type, not an integer index. The order
 *  in which you traverse a hash by either key or value may seem
 *  arbitrary, and will generally not be in the insertion order.
 *
 *  Hashes have a <em>default value</em> that is returned when accessing
 *  keys that do not exist in the hash. By default, that value is
 *  <code>nil</code>.
 *
 */

void Init_NSDictionary(void);

void
Init_Hash(void)
{
    Init_NSDictionary();

    selFlattenBang = sel_registerName("flatten!:");
    selDefault = sel_registerName("default:");
    selHash = sel_registerName("hash");

    id_yield = rb_intern("yield");

    rb_cRubyHash = rb_define_class("Hash", rb_cNSMutableHash);
    rb_objc_install_NSObject_special_methods((Class)rb_cRubyHash);

    rb_objc_define_method(*(VALUE *)rb_cRubyHash, "new",
	    rb_class_new_instance_imp, -1);
    rb_objc_define_method(*(VALUE *)rb_cRubyHash, "alloc", rhash_alloc, 0);
    rb_objc_define_method(*(VALUE *)rb_cRubyHash, "[]", rhash_create, -1);
    rb_objc_define_method(*(VALUE *)rb_cRubyHash, "try_convert",
	    rhash_try_convert, 1);
    rb_objc_define_method(rb_cRubyHash, "initialize", rhash_initialize, -1);
    rb_objc_define_method(rb_cRubyHash, "initialize_copy", rhash_replace, 1);
    rb_objc_define_method(rb_cRubyHash, "dup", rhash_dup, 0);
    rb_objc_define_method(rb_cRubyHash, "rehash", rhash_rehash, 0);
    rb_objc_define_method(rb_cRubyHash, "to_hash", rhash_to_hash, 0);
    rb_objc_define_method(rb_cRubyHash, "to_a", rhash_to_a, 0);
    rb_objc_define_method(rb_cRubyHash, "to_s", rhash_inspect, 0);
    rb_objc_define_method(rb_cRubyHash, "inspect", rhash_inspect, 0);
    rb_objc_define_method(rb_cRubyHash, "==", rhash_equal, 1);
    rb_objc_define_method(rb_cRubyHash, "[]", rhash_aref, 1);
    rb_objc_define_method(rb_cRubyHash, "eql?", rhash_eql, 1);
    rb_objc_define_method(rb_cRubyHash, "fetch", rhash_fetch, -1);
    rb_objc_define_method(rb_cRubyHash, "[]=", rhash_aset, 2);
    rb_objc_define_method(rb_cRubyHash, "store", rhash_aset, 2);
    rb_objc_define_method(rb_cRubyHash, "default", rhash_default, -1);
    rb_objc_define_method(rb_cRubyHash, "default=", rhash_set_default, 1);
    rb_objc_define_method(rb_cRubyHash, "default_proc",
	    rhash_default_proc, 0);
    rb_objc_define_method(rb_cRubyHash, "default_proc=",
	    rhash_set_default_proc, 1);
    rb_objc_define_method(rb_cRubyHash, "key", rhash_key, 1);
    rb_objc_define_method(rb_cRubyHash, "index", rhash_index, 1);
    rb_objc_define_method(rb_cRubyHash, "size", rhash_size, 0);
    rb_objc_define_method(rb_cRubyHash, "length", rhash_size, 0);
    rb_objc_define_method(rb_cRubyHash, "empty?", rhash_empty, 0);
    rb_objc_define_method(rb_cRubyHash, "each_value", rhash_each_value, 0);
    rb_objc_define_method(rb_cRubyHash, "each_key", rhash_each_key, 0);
    rb_objc_define_method(rb_cRubyHash, "each_pair", rhash_each_pair, 0);
    rb_objc_define_method(rb_cRubyHash, "each", rhash_each_pair, 0);
    rb_objc_define_method(rb_cRubyHash, "keys", rhash_keys, 0);
    rb_objc_define_method(rb_cRubyHash, "values", rhash_values, 0);
    rb_objc_define_method(rb_cRubyHash, "values_at", rhash_values_at, -1);
    rb_objc_define_method(rb_cRubyHash, "shift", rhash_shift, 0);
    rb_objc_define_method(rb_cRubyHash, "delete", rhash_delete, 1);
    rb_objc_define_method(rb_cRubyHash, "delete_if", rhash_delete_if, 0);
    rb_objc_define_method(rb_cRubyHash, "keep_if", rhash_keep_if, 0);
    rb_objc_define_method(rb_cRubyHash, "select", rhash_select, 0);
    rb_objc_define_method(rb_cRubyHash, "select!", rhash_select_bang, 0);
    rb_objc_define_method(rb_cRubyHash, "reject", rhash_reject, 0);
    rb_objc_define_method(rb_cRubyHash, "reject!", rhash_reject_bang, 0);
    rb_objc_define_method(rb_cRubyHash, "clear", rhash_clear, 0);
    rb_objc_define_method(rb_cRubyHash, "invert", rhash_invert, 0);
    rb_objc_define_method(rb_cRubyHash, "update", rhash_update, 1);
    rb_objc_define_method(rb_cRubyHash, "replace", rhash_replace, 1);
    rb_objc_define_method(rb_cRubyHash, "merge!", rhash_update, 1);
    rb_objc_define_method(rb_cRubyHash, "merge", rhash_merge, 1);
    rb_objc_define_method(rb_cRubyHash, "assoc", rhash_assoc, 1);
    rb_objc_define_method(rb_cRubyHash, "rassoc", rhash_rassoc, 1);
    rb_objc_define_method(rb_cRubyHash, "flatten", rhash_flatten, -1);
    rb_objc_define_method(rb_cRubyHash, "include?", rhash_has_key, 1);
    rb_objc_define_method(rb_cRubyHash, "member?", rhash_has_key, 1);
    rb_objc_define_method(rb_cRubyHash, "has_key?", rhash_has_key, 1);
    rb_objc_define_method(rb_cRubyHash, "has_value?", rhash_has_value, 1);
    rb_objc_define_method(rb_cRubyHash, "key?", rhash_has_key, 1);
    rb_objc_define_method(rb_cRubyHash, "value?", rhash_has_value, 1);
    rb_objc_define_method(rb_cRubyHash, "compare_by_identity",
	    rhash_compare_by_id, 0);
    rb_objc_define_method(rb_cRubyHash, "compare_by_identity?",
	    rhash_compare_by_id_p, 0);

    rb_objc_install_method2((Class)rb_cRubyHash, "count",
	    (IMP)imp_rhash_count);
    rb_objc_install_method2((Class)rb_cRubyHash, "objectForKey:",
	    (IMP)imp_rhash_objectForKey);
    rb_objc_install_method2((Class)rb_cRubyHash, "keyEnumerator",
	    (IMP)imp_rhash_keyEnumerator);
    rb_objc_install_method2((Class)rb_cRubyHash, "setObject:forKey:",
	    (IMP)imp_rhash_setObjectForKey);
    rb_objc_install_method2((Class)rb_cRubyHash, "removeObjectForKey:",
	    (IMP)imp_rhash_removeObjectForKey);

    VALUE NSEnumerator = (VALUE)objc_getClass("NSEnumerator");
    assert(NSEnumerator != 0);
    rb_cRubyHashKeyEnumerator = rb_define_class("RubyHashKeyEnumerator",
	NSEnumerator);
    rb_objc_install_method2((Class)rb_cRubyHashKeyEnumerator, "allObjects",
	(IMP)imp_rhash_keyenum_allObjects);
    rb_objc_install_method2((Class)rb_cRubyHashKeyEnumerator, "nextObject",
	(IMP)imp_rhash_keyenum_nextObject);
}