Rollup merge of #64255 - varkor:bool-to-option, r=Centril

Add methods for converting `bool` to `Option<T>`

This provides a reference implementation for https://github.com/rust-lang/rfcs/pull/2757.

4 files changed, 55 insertions, 0 deletions

diff --git a/src/libcore/bool.rs b/src/libcore/bool.rs
new file mode 100644
index 00000000000..32ec26975e3
--- /dev/null
+++ b/src/libcore/bool.rs
@@ -0,0 +1,45 @@
+//! impl bool {}
+
+#[cfg(not(boostrap_stdarch_ignore_this))]
+#[lang = "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 = "64260")]
+    #[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 = "64260")]
+    #[inline]
+    pub fn then_with<T, F: FnOnce() -> T>(self, f: F) -> Option<T> {
+        if self {
+            Some(f())
+        } else {
+            None
+        }
+    }
+}
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index c168d5c8a2e..690cff483b0 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -227,6 +227,7 @@ pub mod task;
 pub mod alloc;
 
 // note: does not need to be public
+mod bool;
 mod tuple;
 mod unit;
 
diff --git a/src/libcore/tests/bool.rs b/src/libcore/tests/bool.rs
new file mode 100644
index 00000000000..0f1e6e89451
--- /dev/null
+++ b/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));
+}
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index a3b108b2e9c..b2c29aa2692 100644
--- a/src/libcore/tests/lib.rs
+++ b/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 any;
 mod array;
 mod ascii;
 mod atomic;
+mod bool;
 mod cell;
 mod char;
 mod clone;