auto merge of #14610 : alexcrichton/rust/issue-14008, r=brson

This commit removes the <M: Any + Send> type parameter from Option::expect in
favor of just taking a hard-coded `&str` argument. This allows this function to
move into libcore.

Previous code using strings with `expect` will continue to work, but code using
this implicitly to transmit task failure will need to unwrap manually with a
`match` statement.

[breaking-change]
Closes #14008

1 files changed, 14 insertions, 0 deletions

diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index b91a8cebded..45ccf657dbd 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -233,6 +233,20 @@ impl<T> Option<T> {
     // Getting to contained values
     /////////////////////////////////////////////////////////////////////////
 
+    /// Unwraps an option, yielding the content of a `Some`
+    ///
+    /// # Failure
+    ///
+    /// Fails if the value is a `None` with a custom failure message provided by
+    /// `msg`.
+    #[inline]
+    pub fn expect(self, msg: &str) -> T {
+        match self {
+            Some(val) => val,
+            None => fail!(msg),
+        }
+    }
+
     /// Moves a value out of an option type and returns it, consuming the `Option`.
     ///
     /// # Failure