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android / platform / external / rust / crates / paste / 1e8b07068e8a586ce0b2d66e46a5d435fdb842f8
commit1e8b07068e8a586ce0b2d66e46a5d435fdb842f8[log] [tgz]
authorJason Macnak <natsu@google.com>Wed Mar 18 02:08:27 2020 +0000
committerJason Macnak <natsu@google.com>Mon Apr 06 10:44:38 2020 -0700
tree771b90bcb706bf560961a9c2f903e18136722d72
parent88c32390b829d0b7083428cefbf5728e2f2860e0 [diff]
Import 'paste' rust crate version 0.1.7

Bug: b/151760391
Test: m crosvm.experimental
Change-Id: I6e9288d1a0c749166c6ce8cf483c7646a70d32b3
14 files changed
tree: 771b90bcb706bf560961a9c2f903e18136722d72
  1. src/
  2. tests/
  3. LICENSE ⇨ LICENSE-APACHE
  4. NOTICE ⇨ LICENSE
  5. .cargo_vcs_info.json
  6. .gitignore
  7. Android.bp
  8. Cargo.toml
  9. Cargo.toml.orig
  10. LICENSE-APACHE
  11. LICENSE-MIT
  12. METADATA
  13. MODULE_LICENSE_APACHE2
  14. README.md
README.md

Macros for all your token pasting needs

Build Status Latest Version Rust Documentation

The nightly-only concat_idents! macro in the Rust standard library is notoriously underpowered in that its concatenated identifiers can only refer to existing items, they can never be used to define something new.

This crate provides a flexible way to paste together identifiers in a macro, including using pasted identifiers to define new items.

[dependencies]
paste = "0.1"

This approach works with any stable or nightly Rust compiler 1.30+.

Pasting identifiers

There are two entry points, paste::expr! for macros in expression position and paste::item! for macros in item position.

Within either one, identifiers inside [<...>] are pasted together to form a single identifier.

// Macro in item position: at module scope or inside of an impl block.
paste::item! {
    // Defines a const called `QRST`.
    const [<Q R S T>]: &str = "success!";
}

fn main() {
    // Macro in expression position: inside a function body.
    assert_eq!(
        paste::expr! { [<Q R S T>].len() },
        8,
    );
}

More elaborate examples

This program demonstrates how you may want to bundle a paste invocation inside of a more convenient user-facing macro of your own. Here the routes!(A, B) macro expands to a vector containing ROUTE_A and ROUTE_B.

const ROUTE_A: &str = "/a";
const ROUTE_B: &str = "/b";

macro_rules! routes {
    ($($route:ident),*) => {{
        paste::expr! {
            vec![$( [<ROUTE_ $route>] ),*]
        }
    }}
}

fn main() {
    let routes = routes!(A, B);
    assert_eq!(routes, vec!["/a", "/b"]);
}

The next example shows a macro that generates accessor methods for some struct fields.

macro_rules! make_a_struct_and_getters {
    ($name:ident { $($field:ident),* }) => {
        // Define a struct. This expands to:
        //
        //     pub struct S {
        //         a: String,
        //         b: String,
        //         c: String,
        //     }
        pub struct $name {
            $(
                $field: String,
            )*
        }

        // Build an impl block with getters. This expands to:
        //
        //     impl S {
        //         pub fn get_a(&self) -> &str { &self.a }
        //         pub fn get_b(&self) -> &str { &self.b }
        //         pub fn get_c(&self) -> &str { &self.c }
        //     }
        paste::item! {
            impl $name {
                $(
                    pub fn [<get_ $field>](&self) -> &str {
                        &self.$field
                    }
                )*
            }
        }
    }
}

make_a_struct_and_getters!(S { a, b, c });

fn call_some_getters(s: &S) -> bool {
    s.get_a() == s.get_b() && s.get_c().is_empty()
}

License