Macros for all your token pasting needs
=======================================
[
](https://github.com/dtolnay/paste)
[
](https://crates.io/crates/paste)
[
](https://docs.rs/paste)
[
](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+.
## 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 []: &str = "success!";
}
fn main() {
assert_eq!(
paste! { [].len() },
8,
);
}
```
## 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 {
$(
pub fn [](&self) -> &str {
&self.$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()
}
```
## 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, `[]` 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
## 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!() }
}
};
}
pub struct Paste {}
method_new!(Paste); // expands to #[doc = "Create a new `Paste` object"]
```
#### License
Licensed under either of Apache License, Version
2.0 or MIT license at your option.
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.