[−][src]Crate partial_application
The partial!
macro allows for partial application of a function.
partial!(some_fn => arg0, _, arg2, _)
returns the closure |x1, x3| some_fn(arg0, x1, arg2, x3)
.
Move closures are created by adding move
in front of the function: partial!(move ..)
#[macro_use] extern crate partial_application; fn foo(a: i32, b: i32, c: i32, d: i32, mul: i32, off: i32) -> i32 { (a + b*b + c.pow(3) + d.pow(4)) * mul - off } fn main() { let bar = partial!(foo => _, _, 10, _, 10, 10); assert_eq!( foo(15, 15, 10, 42, 10, 10), bar(15, 15, 42) ); }
The expressions used to fix an argument are reevaluated on every call of the new function because of the straightforward translation behind the macro.
fn identity(x: u32) -> u32 { x } let mut n = 0; let mut f = partial!(identity => { n += 1; n}); assert_eq!(f(), 1); assert_eq!(f(), 2);
Pre-compute arguments to be fixed in a local variable, if their creation is expensive or has unwanted side-effects.
You can also use a comma (,
) or semicolon (;
) instead of the arrow (=>
).
This strange syntax choice is due to limitations imposed on us by the macro system.
No other tokens may follow the expression token for the function.
Macros
partial | The macro that creates a wrapping closure for a partially applied function |