Add bool::then and bool::then_with

src/libcore/bool/mod.rs

@@ -4,4 +4,44 @@
 
 #[cfg(not(boostrap_stdarch_ignore_this))]
 #[lang = "bool"]
-impl bool {}
+impl bool {
+    /// Returns `Some(t)` if the `bool` is `true`, or `None` otherwise.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(bool_to_option)]
+    ///
+    /// assert_eq!(false.then(0), None);
+    /// assert_eq!(true.then(0), Some(0));
+    /// ```
+    #[unstable(feature = "bool_to_option", issue = "0")]
+    #[inline]
+    pub fn then<T>(self, t: T) -> Option<T> {
+        if self {
+            Some(t)
+        } else {
+            None
+        }
+    }
+
+    /// Returns `Some(f())` if the `bool` is `true`, or `None` otherwise.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(bool_to_option)]
+    ///
+    /// assert_eq!(false.then_with(|| 0), None);
+    /// assert_eq!(true.then_with(|| 0), Some(0));
+    /// ```
+    #[unstable(feature = "bool_to_option", issue = "0")]
+    #[inline]
+    pub fn then_with<T, F: FnOnce() -> T>(self, f: F) -> Option<T> {
+        if self {
+            Some(f())
+        } else {
+            None
+        }
+    }
+}

src/libcore/tests/bool.rs

@@ -0,0 +1,7 @@
+#[test]
+fn test_bool_to_option() {
+    assert_eq!(false.then(0), None);
+    assert_eq!(true.then(0), Some(0));
+    assert_eq!(false.then_with(|| 0), None);
+    assert_eq!(true.then_with(|| 0), Some(0));
+}

src/libcore/tests/lib.rs

@@ -1,3 +1,4 @@
+#![feature(bool_to_option)]
 #![feature(bound_cloned)]
 #![feature(box_syntax)]
 #![feature(cell_update)]
@@ -40,6 +41,7 @@
 mod array;
 mod ascii;
 mod atomic;
+mod bool;
 mod cell;
 mod char;
 mod clone;