Rollup merge of #36396 - athulappadan:Default-docs, r=bluss

Documentation of what Default does for each type

Addresses #36265
I haven't changed the following types due to doubts:

1)src/libstd/ffi/c_str.rs
2)src/libcore/iter/sources.rs
3)src/libcore/hash/mod.rs
4)src/libcore/hash/mod.rs
5)src/librustc/middle/privacy.rs

r? @steveklabnik

6 files changed, 10 insertions, 0 deletions

diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index f0710a1d935..51221f1b9b9 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -317,6 +317,7 @@ impl<T:Copy> Clone for Cell<T> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T:Default + Copy> Default for Cell<T> {
+    /// Creates a `Cell<T>`, with the `Default` value for T.
     #[inline]
     fn default() -> Cell<T> {
         Cell::new(Default::default())
@@ -758,6 +759,7 @@ impl<T: Clone> Clone for RefCell<T> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T:Default> Default for RefCell<T> {
+    /// Creates a `RefCell<T>`, with the `Default` value for T.
     #[inline]
     fn default() -> RefCell<T> {
         RefCell::new(Default::default())
@@ -1139,6 +1141,7 @@ impl<T: ?Sized> UnsafeCell<T> {
 
 #[stable(feature = "unsafe_cell_default", since = "1.9.0")]
 impl<T: Default> Default for UnsafeCell<T> {
+    /// Creates an `UnsafeCell`, with the `Default` value for T.
     fn default() -> UnsafeCell<T> {
         UnsafeCell::new(Default::default())
     }
diff --git a/src/libcore/hash/sip.rs b/src/libcore/hash/sip.rs
index bd6cae92b05..dc53683d633 100644
--- a/src/libcore/hash/sip.rs
+++ b/src/libcore/hash/sip.rs
@@ -333,6 +333,7 @@ impl<S: Sip> Clone for Hasher<S> {
 }
 
 impl<S: Sip> Default for Hasher<S> {
+    /// Creates a `Hasher<S>` with the two initial keys set to 0.
     #[inline]
     fn default() -> Hasher<S> {
         Hasher::new_with_keys(0, 0)
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index dacb396ee40..b9fb2dc90c7 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -714,6 +714,7 @@ fn expect_failed(msg: &str) -> ! {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Default for Option<T> {
+    /// Returns None.
     #[inline]
     fn default() -> Option<T> { None }
 }
diff --git a/src/libcore/slice.rs b/src/libcore/slice.rs
index b22bdb43414..7b147faccd2 100644
--- a/src/libcore/slice.rs
+++ b/src/libcore/slice.rs
@@ -755,11 +755,13 @@ impl<T> ops::IndexMut<ops::RangeToInclusive<usize>> for [T] {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> Default for &'a [T] {
+    /// Creates an empty slice.
     fn default() -> &'a [T] { &[] }
 }
 
 #[stable(feature = "mut_slice_default", since = "1.5.0")]
 impl<'a, T> Default for &'a mut [T] {
+    /// Creates a mutable empty slice.
     fn default() -> &'a mut [T] { &mut [] }
 }
 
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index 18e43c02c64..1f1ae6f12ab 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -1987,5 +1987,6 @@ impl AsRef<[u8]> for str {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Default for &'a str {
+    /// Creates an empty str
     fn default() -> &'a str { "" }
 }
diff --git a/src/libcore/sync/atomic.rs b/src/libcore/sync/atomic.rs
index 75ddd2021a8..f5f37be52de 100644
--- a/src/libcore/sync/atomic.rs
+++ b/src/libcore/sync/atomic.rs
@@ -95,6 +95,7 @@ pub struct AtomicBool {
 #[cfg(target_has_atomic = "8")]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Default for AtomicBool {
+    /// Creates an `AtomicBool` initialised as false.
     fn default() -> Self {
         Self::new(false)
     }
@@ -117,6 +118,7 @@ pub struct AtomicPtr<T> {
 #[cfg(target_has_atomic = "ptr")]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Default for AtomicPtr<T> {
+    /// Creates a null `AtomicPtr<T>`.
     fn default() -> AtomicPtr<T> {
         AtomicPtr::new(::ptr::null_mut())
     }