Merge #377 #381

377: Add Itertools::filter_{,map_}results r=jswrenn a=gin-ahirsch

I found myself wanting `filter_map_results()` and just implemented `filter_results()` in the same stretch. I hope you find it useful!

I wasn't sure if #236 applies to these new iterators; I just implemented them.

381: Add Itertools::intersperse_with r=jswrenn a=gin-ahirsch

Pretty self-explanatory. Useful for non-clonable elements or otherwise stateful interspersing.
`intersperse()` could be implemented via `intersperse_with()`, allowing the change to be more minimal. I haven't done it currently, but if you don't see any downsides I'd amend this change to do `self.intersperse_with(|| element)` for `intersperse()` instead.

Co-authored-by: Alexander Hirsch <alexander.hirsch@gin.de>

src/adaptors/mod.rs

@@ -1086,28 +1086,31 @@ where
     I::Item: Into<R>,
 {}
 
-/// An iterator adapter to apply a transformation within a nested `Result`.
+#[deprecated(note="Use MapOk instead", since="0.10")]
+pub type MapResults<I, F> = MapOk<I, F>;
+
+/// An iterator adapter to apply a transformation within a nested `Result::Ok`.
 ///
-/// See [`.map_results()`](../trait.Itertools.html#method.map_results) for more information.
+/// See [`.map_ok()`](../trait.Itertools.html#method.map_ok) for more information.
 #[derive(Clone)]
 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
-pub struct MapResults<I, F> {
+pub struct MapOk<I, F> {
     iter: I,
     f: F
 }
 
-/// Create a new `MapResults` iterator.
-pub fn map_results<I, F, T, U, E>(iter: I, f: F) -> MapResults<I, F>
+/// Create a new `MapOk` iterator.
+pub fn map_ok<I, F, T, U, E>(iter: I, f: F) -> MapOk<I, F>
     where I: Iterator<Item = Result<T, E>>,
           F: FnMut(T) -> U,
 {
-    MapResults {
+    MapOk {
         iter,
         f,
     }
 }
 
-impl<I, F, T, U, E> Iterator for MapResults<I, F>
+impl<I, F, T, U, E> Iterator for MapOk<I, F>
     where I: Iterator<Item = Result<T, E>>,
           F: FnMut(T) -> U,
 {
@@ -1136,6 +1139,141 @@ impl<I, F, T, U, E> Iterator for MapResults<I, F>
     }
 }
 
+/// An iterator adapter to filter values within a nested `Result::Ok`.
+///
+/// See [`.filter_ok()`](../trait.Itertools.html#method.filter_ok) for more information.
+#[derive(Clone)]
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct FilterOk<I, F> {
+    iter: I,
+    f: F
+}
+
+/// Create a new `FilterOk` iterator.
+pub fn filter_ok<I, F, T, E>(iter: I, f: F) -> FilterOk<I, F>
+    where I: Iterator<Item = Result<T, E>>,
+          F: FnMut(&T) -> bool,
+{
+    FilterOk {
+        iter,
+        f,
+    }
+}
+
+impl<I, F, T, E> Iterator for FilterOk<I, F>
+    where I: Iterator<Item = Result<T, E>>,
+          F: FnMut(&T) -> bool,
+{
+    type Item = Result<T, E>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match self.iter.next() {
+                Some(Ok(v)) => {
+                    if (self.f)(&v) {
+                        return Some(Ok(v));
+                    }
+                },
+                Some(Err(e)) => return Some(Err(e)),
+                None => return None,
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.iter.size_hint().1)
+    }
+
+    fn fold<Acc, Fold>(self, init: Acc, fold_f: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.filter(|v| {
+            v.as_ref().map(&mut f).unwrap_or(true)
+        }).fold(init, fold_f)
+    }
+
+    fn collect<C>(self) -> C
+        where C: FromIterator<Self::Item>
+    {
+        let mut f = self.f;
+        self.iter.filter(|v| {
+            v.as_ref().map(&mut f).unwrap_or(true)
+        }).collect()
+    }
+}
+
+/// An iterator adapter to filter and apply a transformation on values within a nested `Result::Ok`.
+///
+/// See [`.filter_map_ok()`](../trait.Itertools.html#method.filter_map_ok) for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct FilterMapOk<I, F> {
+    iter: I,
+    f: F
+}
+
+fn transpose_result<T, E>(result: Result<Option<T>, E>) -> Option<Result<T, E>> {
+    match result {
+        Ok(Some(v)) => Some(Ok(v)),
+        Ok(None) => None,
+        Err(e) => Some(Err(e)),
+    }
+}
+
+/// Create a new `FilterOk` iterator.
+pub fn filter_map_ok<I, F, T, U, E>(iter: I, f: F) -> FilterMapOk<I, F>
+    where I: Iterator<Item = Result<T, E>>,
+          F: FnMut(T) -> Option<U>,
+{
+    FilterMapOk {
+        iter,
+        f,
+    }
+}
+
+impl<I, F, T, U, E> Iterator for FilterMapOk<I, F>
+    where I: Iterator<Item = Result<T, E>>,
+          F: FnMut(T) -> Option<U>,
+{
+    type Item = Result<U, E>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match self.iter.next() {
+                Some(Ok(v)) => {
+                    if let Some(v) = (self.f)(v) {
+                        return Some(Ok(v));
+                    }
+                },
+                Some(Err(e)) => return Some(Err(e)),
+                None => return None,
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.iter.size_hint().1)
+    }
+
+    fn fold<Acc, Fold>(self, init: Acc, fold_f: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.filter_map(|v| {
+            transpose_result(v.map(&mut f))
+        }).fold(init, fold_f)
+    }
+
+    fn collect<C>(self) -> C
+        where C: FromIterator<Self::Item>
+    {
+        let mut f = self.f;
+        self.iter.filter_map(|v| {
+            transpose_result(v.map(&mut f))
+        }).collect()
+    }
+}
+
 /// An iterator adapter to get the positions of each element that matches a predicate.
 ///
 /// See [`.positions()`](../trait.Itertools.html#method.positions) for more information.

src/intersperse.rs

@@ -1,7 +1,6 @@
 use std::iter::Fuse;
 use super::size_hint;
 
-#[derive(Clone)]
 /// An iterator adaptor to insert a particular value
 /// between each element of the adapted iterator.
 ///
@@ -11,7 +10,7 @@ use super::size_hint;
 ///
 /// See [`.intersperse()`](../trait.Itertools.html#method.intersperse) for more information.
 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct Intersperse<I>
     where I: Iterator
 {
@@ -62,7 +61,7 @@ impl<I> Iterator for Intersperse<I>
         Self: Sized, F: FnMut(B, Self::Item) -> B,
     {
         let mut accum = init;
-        
+
         if let Some(x) = self.peek.take() {
             accum = f(accum, x);
         }
@@ -77,3 +76,81 @@ impl<I> Iterator for Intersperse<I>
         })
     }
 }
+
+/// An iterator adaptor to insert a particular value created by a function
+/// between each element of the adapted iterator.
+///
+/// Iterator element type is `I::Item`
+///
+/// This iterator is *fused*.
+///
+/// See [`.intersperse_with()`](../trait.Itertools.html#method.intersperse_with) for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Clone, Debug)]
+pub struct IntersperseWith<I, ElemF>
+    where I: Iterator,
+    ElemF: FnMut() -> I::Item,
+{
+    element: ElemF,
+    iter: Fuse<I>,
+    peek: Option<I::Item>,
+}
+
+/// Create a new IntersperseWith iterator
+pub fn intersperse_with<I, ElemF>(iter: I, elt: ElemF) -> IntersperseWith<I, ElemF>
+    where I: Iterator,
+    ElemF: FnMut() -> I::Item
+{
+    let mut iter = iter.fuse();
+    IntersperseWith {
+        peek: iter.next(),
+        iter: iter,
+        element: elt,
+    }
+}
+
+impl<I, ElemF> Iterator for IntersperseWith<I, ElemF>
+    where I: Iterator,
+          ElemF: FnMut() -> I::Item
+{
+    type Item = I::Item;
+    #[inline]
+    fn next(&mut self) -> Option<I::Item> {
+        if self.peek.is_some() {
+            self.peek.take()
+        } else {
+            self.peek = self.iter.next();
+            if self.peek.is_some() {
+                Some((self.element)())
+            } else {
+                None
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        // 2 * SH + { 1 or 0 }
+        let has_peek = self.peek.is_some() as usize;
+        let sh = self.iter.size_hint();
+        size_hint::add_scalar(size_hint::add(sh, sh), has_peek)
+    }
+
+    fn fold<B, F>(mut self, init: B, mut f: F) -> B where
+        Self: Sized, F: FnMut(B, Self::Item) -> B,
+    {
+        let mut accum = init;
+
+        if let Some(x) = self.peek.take() {
+            accum = f(accum, x);
+        }
+
+        let element = &mut self.element;
+
+        self.iter.fold(accum,
+            |accum, x| {
+                let accum = f(accum, (element)());
+                let accum = f(accum, x);
+                accum
+        })
+    }
+}