An attribute for deprecation - The Edition Guide

# An attribute for deprecation

If you're writing a library, and you'd like to deprecate something, you can use the `deprecated` attribute:

    #![allow(unused_variables)]
    fn main() {
    #[deprecated(
        since = "0.2.1",
        note = "Please use the bar function instead"
    )]
    pub fn foo() {
        // ...
    }
    }

This will give your users a warning if they use the deprecated functionality:

       Compiling playground v0.0.1 (file:///playground)
    warning: use of deprecated item 'foo': Please use the bar function instead
      --> src/main.rs:10:5
       |
    10 |     foo();
       |     ^^^
       |
       = note: #[warn(deprecated)] on by default

Both `since` and `note` are optional.

`since` can be in the future; you can put whatever you'd like, and what's put in there isn't checked.