std: Remove extra type params on iter adaptors

Now that associated types are fully implemented the iterator adaptors only need
type parameters which are associated with actual storage. All other type
parameters can either be derived from these (e.g. they are an associated type)
or can be bare on the `impl` block itself.

This is a breaking change due to the removal of type parameters on these
iterator adaptors, but code can fairly easily migrate by just deleting the
relevant type parameters for each adaptor. Other behavior should not be
affected.

Closes #21839
[breaking-change]

4 files changed, 9 insertions, 19 deletions

diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index 3e2c7627dbe..852d5a86fc0 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -1300,18 +1300,13 @@ pub struct IterMut<'a, K: 'a, V: 'a> {
 /// HashMap move iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoIter<K, V> {
-    inner: iter::Map<
-        (SafeHash, K, V),
-        (K, V),
-        table::IntoIter<K, V>,
-        fn((SafeHash, K, V)) -> (K, V),
-    >
+    inner: iter::Map<table::IntoIter<K, V>, fn((SafeHash, K, V)) -> (K, V)>
 }
 
 /// HashMap keys iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Keys<'a, K: 'a, V: 'a> {
-    inner: Map<(&'a K, &'a V), &'a K, Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a K>
+    inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a K>
 }
 
 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
@@ -1326,7 +1321,7 @@ impl<'a, K, V> Clone for Keys<'a, K, V> {
 /// HashMap values iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Values<'a, K: 'a, V: 'a> {
-    inner: Map<(&'a K, &'a V), &'a V, Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a V>
+    inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a V>
 }
 
 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
@@ -1342,12 +1337,7 @@ impl<'a, K, V> Clone for Values<'a, K, V> {
 #[unstable(feature = "std_misc",
            reason = "matches collection reform specification, waiting for dust to settle")]
 pub struct Drain<'a, K: 'a, V: 'a> {
-    inner: iter::Map<
-        (SafeHash, K, V),
-        (K, V),
-        table::Drain<'a, K, V>,
-        fn((SafeHash, K, V)) -> (K, V),
-    >
+    inner: iter::Map<table::Drain<'a, K, V>, fn((SafeHash, K, V)) -> (K, V)>
 }
 
 /// A view into a single occupied location in a HashMap.
diff --git a/src/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs
index c6dcb0d230f..e6b06e5ef1f 100644
--- a/src/libstd/collections/hash/set.rs
+++ b/src/libstd/collections/hash/set.rs
@@ -794,13 +794,13 @@ pub struct Iter<'a, K: 'a> {
 /// HashSet move iterator
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoIter<K> {
-    iter: Map<(K, ()), K, map::IntoIter<K, ()>, fn((K, ())) -> K>
+    iter: Map<map::IntoIter<K, ()>, fn((K, ())) -> K>
 }
 
 /// HashSet drain iterator
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Drain<'a, K: 'a> {
-    iter: Map<(K, ()), K, map::Drain<'a, K, ()>, fn((K, ())) -> K>,
+    iter: Map<map::Drain<'a, K, ()>, fn((K, ())) -> K>,
 }
 
 /// Intersection iterator
diff --git a/src/libstd/path/posix.rs b/src/libstd/path/posix.rs
index 6a0c8a93010..69f815e3f8b 100644
--- a/src/libstd/path/posix.rs
+++ b/src/libstd/path/posix.rs
@@ -31,7 +31,7 @@ pub type Components<'a> = Split<'a, u8, fn(&u8) -> bool>;
 
 /// Iterator that yields successive components of a Path as Option<&str>
 pub type StrComponents<'a> =
-    Map<&'a [u8], Option<&'a str>, Components<'a>, fn(&[u8]) -> Option<&str>>;
+    Map<Components<'a>, fn(&[u8]) -> Option<&str>>;
 
 /// Represents a POSIX file path
 #[derive(Clone)]
diff --git a/src/libstd/path/windows.rs b/src/libstd/path/windows.rs
index b524b89ef9f..750af47ff8c 100644
--- a/src/libstd/path/windows.rs
+++ b/src/libstd/path/windows.rs
@@ -40,11 +40,11 @@ use super::{contains_nul, BytesContainer, GenericPath, GenericPathUnsafe};
 /// Each component is yielded as Option<&str> for compatibility with PosixPath, but
 /// every component in WindowsPath is guaranteed to be Some.
 pub type StrComponents<'a> =
-    Map<&'a str, Option<&'a str>, SplitTerminator<'a, char>, fn(&'a str) -> Option<&'a str>>;
+    Map<SplitTerminator<'a, char>, fn(&'a str) -> Option<&'a str>>;
 
 /// Iterator that yields successive components of a Path as &[u8]
 pub type Components<'a> =
-    Map<Option<&'a str>, &'a [u8], StrComponents<'a>, fn(Option<&str>) -> &[u8]>;
+    Map<StrComponents<'a>, fn(Option<&str>) -> &[u8]>;
 
 /// Represents a Windows path
 // Notes for Windows path impl: