added DerefOption and DerefResult + tests to std

Author: Xandkeeper

src/libcore/option.rs

@@ -146,7 +146,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use iter::{FromIterator, FusedIterator, TrustedLen};
-use {mem, ops};
+use {mem, ops::{self, Deref}};
 
 // Note that this is not a lang item per se, but it has a hidden dependency on
 // `Iterator`, which is one. The compiler assumes that the `next` method of
@@ -914,7 +914,6 @@ fn expect_failed(msg: &str) -> ! {
     panic!("{}", msg)
 }
 
-
 /////////////////////////////////////////////////////////////////////////////
 // Trait implementations
 /////////////////////////////////////////////////////////////////////////////
@@ -979,6 +978,24 @@ impl<T> From<T> for Option<T> {
     }
 }
 
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+/// Extension trait to get a reference of an Option via the Deref trait.
+pub trait OptionDeref<T: Deref> {
+    /// Converts from `&Option<T>` to `Option<&T::Target>`.
+    ///
+    /// Leaves the original Option in-place, creating a new one with a reference
+    /// to the original one, additionally coercing the contents via `Deref`.
+    fn deref(&self) -> Option<&T::Target>;
+}
+
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+impl<T: Deref> OptionDeref<T> for Option<T>
+{
+    fn deref(&self) -> Option<&T::Target> {
+        self.as_ref().map(|t| t.deref())
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Option Iterators
 /////////////////////////////////////////////////////////////////////////////

src/libcore/result.rs

@@ -242,7 +242,7 @@
 
 use fmt;
 use iter::{FromIterator, FusedIterator, TrustedLen};
-use ops;
+use ops::{self, Deref};
 
 /// `Result` is a type that represents either success ([`Ok`]) or failure ([`Err`]).
 ///
@@ -999,6 +999,63 @@ impl<'a, T, E> IntoIterator for &'a mut Result<T, E> {
     }
 }
 
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+/// Extension trait to get a reference to a Result via the Deref trait.
+pub trait ResultDeref<T, E> {
+    /// Converts from `&Result<T, E>` to `Result<&T::Target, &E>`.
+    ///
+    /// Leaves the original Result in-place, creating a new one with a reference
+    /// to the original one, additionally coercing the `Ok` arm of the Result via
+    /// `Deref`.
+    fn deref_ok(&self) -> Result<&T::Target, &E>
+                where
+                       T: Deref;
+
+    /// Converts from `&Result<T, E>` to `Result<&T, &E::Target>`.
+    ///
+    /// Leaves the original Result in-place, creating a new one with a reference
+    /// to the original one, additionally coercing the `Err` arm of the Result via
+    /// `Deref`.
+    fn deref_err(&self) -> Result<&T, &E::Target>
+                 where
+                        E: Deref;
+
+    /// Converts from `&Result<T, E>` to `Result<&T::Target, &E::Target>`.
+    ///
+    /// Leaves the original Result in-place, creating a new one with a reference
+    /// to the original one, additionally coercing both the `Ok` and `Err` arms
+    /// of the Result via `Deref`.
+    fn deref(&self) -> Result<&T::Target, &E::Target>
+             where
+                    T: Deref,
+                    E: Deref;
+}
+
+#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+impl<T, E> ResultDeref<T, E> for Result<T, E> {
+    fn deref_ok(&self) -> Result<&T::Target, &E>
+                where
+                       T: Deref,
+    {
+        self.as_ref().map(|t| t.deref())
+    }
+
+    fn deref_err(&self) -> Result<&T, &E::Target>
+                 where
+                        E: Deref,
+    {
+        self.as_ref().map_err(|e| e.deref())
+    }
+
+    fn deref(&self) -> Result<&T::Target, &E::Target>
+             where
+                    T: Deref,
+                    E: Deref,
+    {
+        self.as_ref().map(|t| t.deref()).map_err(|e| e.deref())
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Result Iterators
 /////////////////////////////////////////////////////////////////////////////

src/libcore/tests/option.rs

@@ -297,3 +297,14 @@ fn test_try() {
     }
     assert_eq!(try_option_err(), Err(NoneError));
 }
+
+#[test]
+fn test_option_deref() {
+    // Some: &Option<T: Deref>::Some(T) -> Option<&T::Deref::Target>::Some(&*T)
+    let ref_option = &Some(&42);
+    assert_eq!(ref_option.deref(), Some(&42));
+
+    // None: &Option<T: Deref>>::None -> None
+    let ref_option = &None;
+    assert_eq!(ref_option.deref(), None);
+}

src/libcore/tests/result.rs

@@ -231,3 +231,24 @@ fn test_try() {
     }
     assert_eq!(try_result_err(), Err(1));
 }
+
+#[test]
+fn test_result_deref() {
+    // Ok(T).deref_ok() -> Result<&T, &E::Deref::Target>::Ok(&T)
+    let ref_ok: &Result<&i32, &u8> = &Ok(&42);
+    assert_eq!(ref_ok.deref_ok(), Ok(&42));
+    assert_eq!(ref_ok.deref_ok(), Ok(&42));
+    assert_eq!(ref_ok.deref(), Ok(&42));
+
+    // Err(E) -> Result<&T, &E::Deref::Target>::Err(&*E)
+    let ref_err: &Result<&i32, &u8> = &Err(&41);
+    assert_eq!(ref_err.deref_err(), Err(&41));
+    assert_eq!(ref_err.deref_err(), Err(&41));
+    assert_eq!(ref_err.deref(), Err(&41));
+
+    // &Ok(T).deref_err() -> Result<&T, &E::Deref::Target>::Ok(&T)
+    assert_eq!(ref_ok.deref_err(), Ok(&&42));
+
+    // &Err(E) -> Result<&T::Deref::Target, &E>::Err(&E)
+    assert_eq!(ref_err.deref_ok(), Err(&&41));
+}