usingnamespace

usingnamespace is a declaration that imports all the public declarations of the operand, which must be a struct, union, or enum, into the current scope:

usingnamespace.zig

usingnamespace @import("std");
test "using std namespace" {
    try testing.expect(true);
}

$ zig test usingnamespace.zig
Test [1/1] test "using std namespace"... 
All 1 tests passed.

usingnamespace can also be used in containers:

usingnamespace_inside_struct.zig

test "using namespace inside struct" {
    const L = struct {
        usingnamespace struct {
            pub fn f() void {}
        };
    };
    L.f();
}

$ zig test usingnamespace_inside_struct.zig
Test [1/1] test "using namespace inside struct"... 
All 1 tests passed.

Instead of the above pattern, it is generally recommended to explicitly alias individual declarations. However, usingnamespace has an important use case when organizing the public API of a file or package. For example, one might have c.zig with all of the C imports:

pub usingnamespace @cImport({
    @cInclude("epoxy/gl.h");
    @cInclude("GLFW/glfw3.h");
    @cDefine("STBI_ONLY_PNG", "");
    @cDefine("STBI_NO_STDIO", "");
    @cInclude("stb_image.h");
});

The above example demonstrates using pub to qualify the usingnamespace additionally makes the imported declarations pub. This can be used to forward declarations, giving precise control over what declarations a given file exposes.