Add initialization helper
When using C libraries, C99 designator list initialization is often times used to initialize data structure. While `std.mem.zeroes` and manually assigning to each field can achieve the same result, it is much more verbose then the equivalent C code: ```zig usingnamespace @cImport({ @cInclude("sokol_app.h"); }); // Using `std.mem.zeroes` and manual assignment. var app_desc = std.mem.zeroes(sapp_desc); app_desc.init_cb = init; app_desc.frame_cb = frame; app_desc.cleanup_cb = cleanup; app_desc.width = 400; app_desc.height = 300; app_desc.window_name = "no default init"; // Using `std.mem.defaultInit`. var app_desc = std.mem.defaultInit(sapp_desc, .{ .init_cb = init, .frame_cb = frame, .cleanup_cb = cleanup, .width = 400, .height = 300, .window_name = "default init" }); ``` The `std.mem.defaultInit` aims to solve this problem by zero initializing all fields of the given struct to their zero, or default value if any. Each field mentionned in the `init` variable is then assigned to the corresponding field in the struct. If a field is a struct, and an initializer for it is present, it is recursively initialized.master
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@ -516,6 +516,80 @@ test "mem.secureZero" {
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testing.expectEqualSlices(u8, a[0..], b[0..]);
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}
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/// Initializes all fields of the struct with their default value, or zero values if no default value is present.
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/// If the field is present in the provided initial values, it will have that value instead.
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/// Structs are initialized recursively.
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pub fn defaultInit(comptime T: type, init: var) T {
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comptime const Init = @TypeOf(init);
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switch (@typeInfo(T)) {
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.Struct => |struct_info| {
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switch (@typeInfo(Init)) {
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.Struct => |init_info| {
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var value = std.mem.zeroes(T);
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inline for (init_info.fields) |field| {
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if (!@hasField(T, field.name)) {
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@compileError("Encountered an initializer for `" ++ field.name ++ "`, but it is not a field of " ++ @typeName(T));
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}
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}
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inline for (struct_info.fields) |field| {
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if (@hasField(Init, field.name)) {
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switch (@typeInfo(field.field_type)) {
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.Struct => {
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@field(value, field.name) = defaultInit(field.field_type, @field(init, field.name));
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},
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else => {
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@field(value, field.name) = @field(init, field.name);
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},
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}
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} else if (field.default_value != null) {
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@field(value, field.name) = field.default_value;
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}
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}
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return value;
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},
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else => {
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@compileError("The initializer must be a struct");
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},
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}
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},
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else => {
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@compileError("Can't default init a " ++ @typeName(T));
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},
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}
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}
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test "mem.defaultInit" {
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const I = struct {
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d: f64,
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};
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const S = struct {
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a: u32,
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b: ?bool,
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c: I,
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e: [3]u8,
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f: i64,
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};
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const s = defaultInit(S, .{
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.a = 42,
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});
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testing.expectEqual(s, S{
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.a = 42,
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.b = null,
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.c = .{
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.d = 0,
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},
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.e = [3]u8{0, 0, 0},
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.f = 0,
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});
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}
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pub fn order(comptime T: type, lhs: []const T, rhs: []const T) math.Order {
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const n = math.min(lhs.len, rhs.len);
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var i: usize = 0;
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