Lazy mutable API extension

CHANGELOG.md

@@ -4,6 +4,13 @@
 
 -
 
+## 1.14.0
+
+- Add extension to `unsync` and `sync` `Lazy` mut API:
+  - `force_mut`
+  - `get_mut`
+
+
 ## 1.13.1
 
 - Make implementation compliant with [strict provenance](https://github.com/rust-lang/rust/issues/95228).

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "once_cell"
-version = "1.13.1"
+version = "1.14.0"
 authors = ["Aleksey Kladov <aleksey.kladov@gmail.com>"]
 license = "MIT OR Apache-2.0"
 edition = "2018"

src/lib.rs

@@ -742,6 +742,25 @@ pub mod unsync {
             })
         }
 
+        /// Forces the evaluation of this lazy value and returns a mutable reference to
+        /// the result.
+        ///
+        /// This is equivalent to the `DerefMut` impl, but is explicit.
+        ///
+        /// # Example
+        /// ```
+        /// use once_cell::unsync::Lazy;
+        ///
+        /// let mut lazy = Lazy::new(|| 92);
+        ///
+        /// assert_eq!(Lazy::force_mut(&mut lazy), &92);
+        /// assert_eq!(*lazy, 92);
+        /// ```
+        pub fn force_mut(this: &mut Lazy<T, F>) -> &mut T {
+            Self::force(this);
+            Self::get_mut(this).unwrap_or_else(|| unreachable!())
+        }
+
         /// Gets the reference to the result of this lazy value if
         /// it was initialized, otherwise returns `None`.
         ///
@@ -758,6 +777,23 @@ pub mod unsync {
         pub fn get(this: &Lazy<T, F>) -> Option<&T> {
             this.cell.get()
         }
+
+        /// Gets the mutable reference to the result of this lazy value if
+        /// it was initialized, otherwise returns `None`.
+        ///
+        /// # Example
+        /// ```
+        /// use once_cell::unsync::Lazy;
+        ///
+        /// let mut lazy = Lazy::new(|| 92);
+        ///
+        /// assert_eq!(Lazy::get_mut(&mut lazy), None);
+        /// assert_eq!(*lazy, 92);
+        /// assert_eq!(Lazy::get_mut(&mut lazy), Some(&mut 92));
+        /// ```
+        pub fn get_mut(this: &mut Lazy<T, F>) -> Option<&mut T> {
+            this.cell.get_mut()
+        }
     }
 
     impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
@@ -1232,6 +1268,23 @@ pub mod sync {
             })
         }
 
+        /// Forces the evaluation of this lazy value and
+        /// returns a mutable reference to the result. This is equivalent
+        /// to the `Deref` impl, but is explicit.
+        ///
+        /// # Example
+        /// ```
+        /// use once_cell::sync::Lazy;
+        ///
+        /// let mut lazy = Lazy::new(|| 92);
+        ///
+        /// assert_eq!(Lazy::force_mut(&mut lazy), &mut 92);
+        /// ```
+        pub fn force_mut(this: &mut Lazy<T, F>) -> &mut T {
+            Self::force(this);
+            Self::get_mut(this).unwrap_or_else(|| unreachable!())
+        }
+
         /// Gets the reference to the result of this lazy value if
         /// it was initialized, otherwise returns `None`.
         ///
@@ -1248,6 +1301,23 @@ pub mod sync {
         pub fn get(this: &Lazy<T, F>) -> Option<&T> {
             this.cell.get()
         }
+
+        /// Gets the reference to the result of this lazy value if
+        /// it was initialized, otherwise returns `None`.
+        ///
+        /// # Example
+        /// ```
+        /// use once_cell::sync::Lazy;
+        ///
+        /// let mut lazy = Lazy::new(|| 92);
+        ///
+        /// assert_eq!(Lazy::get_mut(&mut lazy), None);
+        /// assert_eq!(&*lazy, &92);
+        /// assert_eq!(Lazy::get_mut(&mut lazy), Some(&mut 92));
+        /// ```
+        pub fn get_mut(this: &mut Lazy<T, F>) -> Option<&mut T> {
+            this.cell.get_mut()
+        }
     }
 
     impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {

tests/it.rs

@@ -137,6 +137,41 @@ mod unsync {
         assert_eq!(called.get(), 1);
     }
 
+    #[test]
+    fn lazy_force_mut() {
+        let called = Cell::new(0);
+        let mut x = Lazy::new(|| {
+            called.set(called.get() + 1);
+            92
+        });
+        assert_eq!(called.get(), 0);
+        let v = Lazy::force_mut(&mut x);
+        assert_eq!(called.get(), 1);
+
+        *v /= 2;
+        assert_eq!(*x, 46);
+        assert_eq!(called.get(), 1);
+    }
+
+    #[test]
+    fn lazy_get_mut() {
+        let called = Cell::new(0);
+        let mut x: Lazy<u32, _> = Lazy::new(|| {
+            called.set(called.get() + 1);
+            92
+        });
+
+        assert_eq!(called.get(), 0);
+        assert_eq!(*x, 92);
+
+        let mut_ref: &mut u32 = Lazy::get_mut(&mut x).unwrap();
+        assert_eq!(called.get(), 1);
+
+        *mut_ref /= 2;
+        assert_eq!(*x, 46);
+        assert_eq!(called.get(), 1);
+    }
+
     #[test]
     fn lazy_default() {
         static CALLED: AtomicUsize = AtomicUsize::new(0);