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Macros for all your token pasting needs
=======================================
[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/paste-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/paste)
[<img alt="crates.io" src="https://img.shields.io/crates/v/paste.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/paste)
[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-paste-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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" height="20">](https://docs.rs/paste)
[<img alt="build status" src="https://img.shields.io/github/workflow/status/dtolnay/paste/CI/master?style=for-the-badge" height="20">](https://github.com/dtolnay/paste/actions?query=branch%3Amaster)
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.
[`concat_idents!`]: https://doc.rust-lang.org/std/macro.concat_idents.html
This crate provides a flexible way to paste together identifiers in a macro,
including using pasted identifiers to define new items.
```toml
[dependencies]
paste = "1.0"
```
This approach works with any Rust compiler 1.31+.
<br>
## Pasting identifiers
Within the `paste!` macro, identifiers inside `[<`...`>]` are pasted together to
form a single identifier.
```rust
use paste::paste;
paste! {
// Defines a const called `QRST`.
const [<Q R S T>]: &str = "success!";
}
fn main() {
assert_eq!(
paste! { [<Q R S T>].len() },
8,
);
}
```
<br>
## More elaborate example
The next example shows a macro that generates accessor methods for some struct
fields. It demonstrates how you might find it useful to bundle a paste
invocation inside of a macro\_rules macro.
```rust
use paste::paste;
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! {
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()
}
```
<br>
## Case conversion
Use `$var:lower` or `$var:upper` in the segment list to convert an interpolated
segment to lower- or uppercase as part of the paste. For example, `[<ld_
$reg:lower _expr>]` would paste to `ld_bc_expr` if invoked with $reg=`Bc`.
Use `$var:snake` to convert CamelCase input to snake\_case.
Use `$var:camel` to convert snake\_case to CamelCase.
These compose, so for example `$var:snake:upper` would give you SCREAMING\_CASE.
The precise Unicode conversions are as defined by [`str::to_lowercase`] and
[`str::to_uppercase`].
[`str::to_lowercase`]: https://doc.rust-lang.org/std/primitive.str.html#method.to_lowercase
[`str::to_uppercase`]: https://doc.rust-lang.org/std/primitive.str.html#method.to_uppercase
<br>
## Pasting documentation strings
Within the `paste!` macro, arguments to a #\[doc ...\] attribute are implicitly
concatenated together to form a coherent documentation string.
```rust
use paste::paste;
macro_rules! method_new {
($ret:ident) => {
paste! {
#[doc = "Create a new `" $ret "` object."]
pub fn new() -> $ret { todo!() }
}
};
}
method_new!(Paste); // expands to #[doc = "Create a new `Paste` object"]
```
<br>
#### License
<sup>
Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
</sup>
<br>
<sub>
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.
</sub>
|
