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lazy-static Use 2018-style absolute paths in examples Apr 29, 2019
Cargo.toml Place each standalone example in a workspace Mar 2, 2019 Typo in lazy-static readme Jan 4, 2018

An example of parsing a custom syntax within a functionlike!(...) procedural macro. Demonstrates how to trigger custom warnings and error messages on individual tokens of the input.

The library implements a lazy_static! macro similar to the one from the real lazy_static crate on

lazy_static! {
    static ref USERNAME: Regex = Regex::new("^[a-z0-9_-]{3,16}$").unwrap();

Compile and run the example by doing cargo run in the directory of the example crate.

The implementation shows how to trigger custom warnings and error messages on the macro input. For example if you try adding an uncreatively named FOO lazy static, the macro will scold you with the following warning.

warning: come on, pick a more creative name
  --> src/
10 |     static ref FOO: String = "lazy_static".to_owned();
   |                ^^^

And if you try to lazily initialize () = (), the macro will outright refuse to compile it for you.

error: I can't think of a legitimate use for lazily initializing the value `()`
  --> src/
10 |     static ref UNIT: () = ();
   |                           ^^
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