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# Designators
The arguments of a macro are prefixed by a dollar sign `$` and type annotated
with a *designator*:
```rust,editable
macro_rules! create_function {
// This macro takes an argument of designator `ident` and
// creates a function named `$func_name`.
// The `ident` designator is used for variable/function names.
($func_name:ident) => {
fn $func_name() {
// The `stringify!` macro converts an `ident` into a string.
println!("You called {:?}()",
stringify!($func_name));
}
};
}
// Create functions named `foo` and `bar` with the above macro.
create_function!(foo);
create_function!(bar);
macro_rules! print_result {
// This macro takes an expression of type `expr` and prints
// it as a string along with its result.
// The `expr` designator is used for expressions.
($expression:expr) => {
// `stringify!` will convert the expression *as it is* into a string.
println!("{:?} = {:?}",
stringify!($expression),
$expression);
};
}
fn main() {
foo();
bar();
print_result!(1u32 + 1);
// Recall that blocks are expressions too!
print_result!({
let x = 1u32;
x * x + 2 * x - 1
});
}
```
These are some of the available designators:
* `block`
* `expr` is used for expressions
* `ident` is used for variable/function names
* `item`
* `literal` is used for literal constants
* `pat` (*pattern*)
* `path`
* `stmt` (*statement*)
* `tt` (*token tree*)
* `ty` (*type*)
* `vis` (*visibility qualifier*)
For a complete list, see the [Rust Reference].
[Rust Reference]: https://doc.rust-lang.org/reference/macros-by-example.html
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