Global Variables

Globals

Noir supports global variables. The global's type must be specified by the user:

global N: Field = 5;

global TUPLE: (Field, Field) = (3, 2);

fn main() {
    assert(N == 5);
    assert(N == TUPLE.0 + TUPLE.1);
}

info

Globals can be defined as any expression, so long as they don't depend on themselves - otherwise there would be a dependency cycle! For example:

global T: u32 = foo(T); // dependency error

If they are initialized to a literal integer, globals can be used to specify an array's length:

global N: u32 = 2;

fn main(y : [Field; N]) {
    assert(y[0] == y[1])
}

A global from another module can be imported or referenced externally like any other name:

global N: Field = 20;

fn main() {
    assert(my_submodule::N != N);
}

mod my_submodule {
    global N: Field = 10;
}

When a global is used, Noir replaces the name with its definition on each occurrence. This means globals defined using function calls will repeat the call each time they're used:

global RESULT: [Field; 100] = foo();

fn foo() -> [Field; 100] { ... }

This is usually fine since Noir will generally optimize any function call that does not refer to a program input into a constant. It should be kept in mind however, if the called function performs side-effects like println, as these will still occur on each use.

Visibility

By default, like functions, globals are private to the module they exist in. You can use pub to make the global public or pub(crate) to make it public to just its crate:

// This global is now public
pub global N: u32 = 5;