Crate var [] [src]

A macro to declare multiple mutable variables in one statement.

var! { ... } is a generalised form of let mut x = ...;, allowing for several mutable variables to be declared and initialised at once, inspired by the keyword of the same name in languages like Nim and C#.

Available on


"var! {"
        identifier (":" type)? "=" expression


  • "..." represents a literal ...
  • (...) is for grouping
  • * is zero-or-more copies of the previous entity, comma separated, with optional trailing comma
  • ? is zero-or-one copies of the pervious entity (i.e. optional)


  • var! should always be invoked with {}s or else one will get compile errors (invoking a macro with () and [] mean the its internals are parsed as an expression, but declaring a variable with let is a statement),
  • an initialising expression is required, unlike conventional let,
  • pattern matching cannot be performed.


#[macro_use] extern crate var;

fn fibonacci(n: u32) -> u64 {
    var! {
        a: u64 = 0,
        b = 1,
    for _ in 0..n {
        let tmp = a + b;
        a = b;
        b = tmp;
    return a

fn main() {
    assert_eq!(fibonacci(10), 55);



Implementation details. Do not use this directly.


The main macro, see crate docs for details.