Implement ignore function on Result. Fixes rust-lang#20949

src/libcore/result.rs

@@ -157,6 +157,17 @@
 //! }
 //! ```
 //!
+//! If you are absolutely sure you want to ignore a result, you must
+//! do so explicitly:
+//!
+//! ```{.no_run}
+//! # use std::io::{File, Open, Write};
+//!
+//! # let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
+//! file.write_line("important message").ignore();
+//! # drop(file);
+//! ```
+//!
 //! # The `try!` macro
 //!
 //! When writing code that calls many functions that return the
@@ -353,6 +364,26 @@ impl<T, E> Result<T, E> {
         }
     }
 
+    /// Ignore this result.
+    ///
+    /// Converts `self` into (), consuming `self`, and
+    /// discarding the value or error.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// let x: Result<uint, &str> = Ok(2);
+    /// x.ignore();
+    /// ```
+    #[inline]
+    #[stable]
+    pub fn ignore(self) {
+        match self {
+            Ok(_)  => (),
+            Err(_) => (),
+        }
+    }
+
     /////////////////////////////////////////////////////////////////////////
     // Adapter for working with references
     /////////////////////////////////////////////////////////////////////////

src/libcoretest/result.rs

@@ -139,3 +139,12 @@ pub fn test_unwrap_or_else_panic() {
     let bad_err: Result<int, &'static str> = Err("Unrecoverable mess.");
     let _ : int = bad_err.unwrap_or_else(handler);
 }
+
+#[test]
+pub fn test_ignore() {
+    let ok: Result<int, &'static str> = Ok(100i);
+    let ok_err: Result<int, &'static str> = Err("Err");
+
+    ok.ignore();
+    ok_err.ignore();
+}