zig/test/cases/undefined.zig

const assert = @import("std").debug.assert;
const mem = @import("std").mem;

fn initStaticArray() -> [10]i32 {
    var array: [10]i32 = undefined;
    array[0] = 1;
    array[4] = 2;
    array[7] = 3;
    array[9] = 4;
    return array;
}
const static_array = initStaticArray();
test "init static array to undefined" {
    assert(static_array[0] == 1);
    assert(static_array[4] == 2);
    assert(static_array[7] == 3);
    assert(static_array[9] == 4);

    comptime {
        assert(static_array[0] == 1);
        assert(static_array[4] == 2);
        assert(static_array[7] == 3);
        assert(static_array[9] == 4);
    }
}

const Foo = struct {
    x: i32,

    fn setFooXMethod(foo: &Foo) {
        foo.x = 3;
    }
};

fn setFooX(foo: &Foo) {
    foo.x = 2;
}

test "assign undefined to struct" {
    comptime {
        var foo: Foo = undefined;
        setFooX(&foo);
        assert(foo.x == 2);
    }
    {
        var foo: Foo = undefined;
        setFooX(&foo);
        assert(foo.x == 2);
    }
}

test "assign undefined to struct with method" {
    comptime {
        var foo: Foo = undefined;
        foo.setFooXMethod();
        assert(foo.x == 3);
    }
    {
        var foo: Foo = undefined;
        foo.setFooXMethod();
        assert(foo.x == 3);
    }
}

test "type name of undefined" {
  const x  = undefined;
  assert(mem.eql(u8, @typeName(@typeOf(x)), "(undefined)"));
}