# 1.40.0[−][src]Macro std::todo

    macro_rules! todo {
        () => { ... };
        ($($arg:tt)+) => { ... };
    }

Indicates unfinished code.

This can be useful if you are prototyping and are just looking to have your code typecheck.

The difference between `unimplemented!` and `todo!` is that while `todo!` conveys an intent of implementing the functionality later and the message is "not yet implemented", `unimplemented!` makes no such claims. Its message is "not implemented". Also some IDEs will mark `todo!`s.

# Panics

This will always `panic!`.

# Examples

Here's an example of some in-progress code. We have a trait `Foo`:

    trait Foo {
        fn bar(&self);
        fn baz(&self);
    }

Run

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!`:

    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(), so this is fine.
    }

Run