Macro std::unimplemented

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

Indicates unfinished code.

This can be useful if you are prototyping and are just looking to have your code type-check, or if you're implementing a trait that requires multiple methods, and you're only planning on using one of them.

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);
}

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 unimplemented!:

struct MyStruct;

impl Foo for MyStruct {
    fn bar(&self) {
        // implementation goes here
    }

    fn baz(&self) {
        // let's not worry about implementing baz() for now
        unimplemented!();
    }
}

fn main() {
    let s = MyStruct;
    s.bar();

    // we aren't even using baz() yet, so this is fine.
}