Macro kas_macros::impl_anon
source · impl_anon!() { /* proc-macro */ }
Expand description
Construct a single-instance struct
Rust doesn’t currently support impl Trait { ... }
expressions
or implicit typing of struct fields. This macro is a hack allowing that.
Example:
use std::fmt;
fn main() {
let world = "world";
let says_hello_world = kas::impl_anon! {
struct(&'static str = world);
impl fmt::Display for Self {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "hello {}", self.0)
}
}
};
assert_eq!(format!("{}", says_hello_world), "hello world");
}
That is, this macro creates an anonymous struct type (must be a struct), which may have trait implementations, then creates an instance of that struct.
Struct fields may have a fixed type or may be generic. Syntax is as follows:
- regular struct:
ident: ty = value
- regular struct:
ident: ty
(usesDefault
to construct value) - tuple struct:
ty = value
- tuple struct:
ty
(usesDefault
to construct value)
The field name, ident
, may be _
(anonymous field).
Refer to examples for usage.