Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Pre-allocate capacity for maps in json! macro. #876

Draft
wants to merge 2 commits into
base: master
Choose a base branch
from
Draft

Pre-allocate capacity for maps in json! macro. #876

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
99629eb
Pre-allocate capacity for maps in json! macro.
zachs18 Apr 5, 2022
e976482
Change map-capacity-counting part of json_internal! macro to not repo…
zachs18 Apr 7, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
116 changes: 115 additions & 1 deletion src/macros.rs
View file
Open in desktop
Expand Up @@ -234,6 +234,119 @@ macro_rules! json_internal {
json_internal!(@object $object ($($key)* $tt) ($($rest)*) ($($rest)*));
};


//////////////////////////////////////////////////////////////////////////
// TT muncher for counting the elements inside of an object {...}.
// Each entry is replaced with `1 + ` (or `1` if it is the last element).
// 0 is inserted if the object has a trailing comma.
//
// Must be invoked as: json_internal!(@object_capacity () ($($tt)*) ($($tt)*))
//
// We require two copies of the input tokens so that we can match on one
// copy and trigger errors on the other copy.
//////////////////////////////////////////////////////////////////////////

// Done.
(@object_capacity () () ()) => {0};

// Current entry followed by trailing comma.
(@object_capacity entry , $($rest:tt)*) => {
1 + json_internal!(@object_capacity () ($($rest)*) ($($rest)*))
};

// Current entry followed by unexpected token. The part that parses the values
// will trigger a reasonable error message; here, we just return 0
// so that there is not a duplicated error message.
(@object_capacity entry $unexpected:tt $($rest:tt)*) => {
0
};

// Insert the last entry without trailing comma.
(@object_capacity entry) => {
1
};

// Next value is `null`.
(@object_capacity ($($key:tt)+) (: null $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity entry $($rest)*)
};

// Next value is `true`.
(@object_capacity ($($key:tt)+) (: true $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity entry $($rest)*)
};

// Next value is `false`.
(@object_capacity ($($key:tt)+) (: false $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity entry $($rest)*)
};

// Next value is an array.
(@object_capacity ($($key:tt)+) (: [$($array:tt)*] $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity entry $($rest)*)
};

// Next value is a map.
(@object_capacity ($($key:tt)+) (: {$($map:tt)*} $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity entry $($rest)*)
};

// Next value is an expression followed by comma.
(@object_capacity ($($key:tt)+) (: $value:expr , $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity entry , $($rest)*)
};

// Last value is an expression with no trailing comma.
(@object_capacity ($($key:tt)+) (: $value:expr) $copy:tt) => {
json_internal!(@object_capacity entry)
};

// Missing value for last entry. The part that parses the values
// will trigger a reasonable error message; here, we just return 0
// so that there is not a duplicated error message.
(@object_capacity ($($key:tt)+) (:) $copy:tt) => {
0
};

// Missing colon and value for last entry. The part that parses the values
// will trigger a reasonable error message; here, we just return 0
// so that there is not a duplicated error message.
(@object_capacity ($($key:tt)+) () $copy:tt) => {
0
};

// Misplaced colon. The part that parses the values
// will trigger a reasonable error message; here, we just return 0
// so that there is not a duplicated error message.
(@object_capacity () (: $($rest:tt)*) ($colon:tt $($copy:tt)*)) => {
0
};

// Found a comma inside a key. The part that parses the values
// will trigger a reasonable error message; here, we just return 0
// so that there is not a duplicated error message.
(@object_capacity ($($key:tt)*) (, $($rest:tt)*) ($comma:tt $($copy:tt)*)) => {
0
};

// Key is fully parenthesized. This is not necessary for counting capacity
// since we don't evaluate $key anyway, so just use the munching below.
// (@object_capacity () (($key:expr) : $($rest:tt)*) $copy:tt) => {
// json_internal!(@object_capacity ($key) (: $($rest)*) (: $($rest)*))
// };

// Refuse to absorb colon token into key expression.
// The part that parses the values will trigger a reasonable error message;
// here, we just return 0 so that there is not a duplicated error message.
(@object_capacity ($($key:tt)*) (: $($unexpected:tt)+) $copy:tt) => {
0
};

// Munch a token into the current key.
(@object_capacity ($($key:tt)*) ($tt:tt $($rest:tt)*) $copy:tt) => {
json_internal!(@object_capacity ($($key)* $tt) ($($rest)*) ($($rest)*))
};

//////////////////////////////////////////////////////////////////////////
// The main implementation.
//
Expand Down Expand Up @@ -266,7 +379,8 @@ macro_rules! json_internal {

({ $($tt:tt)+ }) => {
$crate::Value::Object({
let mut object = $crate::Map::new();
let capacity = json_internal!(@object_capacity () ($($tt)+) ($($tt)+));
let mut object = $crate::Map::with_capacity(capacity);
json_internal!(@object object () ($($tt)+) ($($tt)+));
object
})
Expand Down