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.


This will always panic!


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

fn main() {
    let s = MyStruct;

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

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.