1 files changed, 59 insertions, 0 deletions
diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index b052f59b0f5..d77936c7ddd 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -559,6 +559,65 @@ macro_rules! unimplemented {
     ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*)));
 }
 
+/// A standardized placeholder for marking unfinished code.
+///
+/// This can be useful if you are prototyping and are just looking to have your
+/// code typecheck. `todo!` works exactly like `unimplemented!`, there only
+/// difference between the two macros is the name.
+///
+/// # Panics
+///
+/// This will always [panic!](macro.panic.html)
+///
+/// # Examples
+///
+/// Here's an example of some in-progress code. We have a trait `Foo`:
+///
+/// ```
+/// trait Foo {
+///     fn bar(&self);
+///     fn baz(&self);
+/// }
+/// ```
+///
+/// We want to implement `Foo` on one of our types, but we also want to work on
+/// just `bar()` first. In order for our code to compile, we need to implement
+/// `baz()`, so we can use `todo!`:
+///
+/// ```
+/// #![feature(todo_macro)]
+///
+/// # trait Foo {
+/// #     fn bar(&self);
+/// #     fn baz(&self);
+/// # }
+/// struct MyStruct;
+///
+/// impl Foo for MyStruct {
+///     fn bar(&self) {
+///         // implementation goes here
+///     }
+///
+///     fn baz(&self) {
+///         // let's not worry about implementing baz() for now
+///         todo!();
+///     }
+/// }
+///
+/// fn main() {
+///     let s = MyStruct;
+///     s.bar();
+///
+///     // we aren't even using baz() yet, so this is fine.
+/// }
+/// ```
+#[macro_export]
+#[unstable(feature = "todo_macro", issue = "59277")]
+macro_rules! todo {
+    () => (panic!("not yet implemented"));
+    ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*)));
+}
+
 /// A macro to create an array of [`MaybeUninit`]
 ///
 /// This macro constructs an uninitialized array of the type `[MaybeUninit<K>; N]`.