Zig DebugAllocator SmpAllocator comptime switch example

build.zig

const std = @import("std");

// Although this function looks imperative, note that its job is to
// declaratively construct a build graph that will be executed by an external
// runner.
pub fn build(b: *std.Build) void {
    // Standard target options allows the person running `zig build` to choose
    // what target to build for. Here we do not override the defaults, which
    // means any target is allowed, and the default is native. Other options
    // for restricting supported target set are available.
    const target = b.standardTargetOptions(.{});

    // Standard optimization options allow the person running `zig build` to select
    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
    // set a preferred release mode, allowing the user to decide how to optimize.
    const optimize = b.standardOptimizeOption(.{});

    // We will also create a module for our other entry point, 'main.zig'.
    const exe_mod = b.createModule(.{
        // `root_source_file` is the Zig "entry point" of the module. If a module
        // only contains e.g. external object files, you can make this `null`.
        // In this case the main source file is merely a path, however, in more
        // complicated build scripts, this could be a generated file.
        .root_source_file = b.path("main.zig"),
        .target = target,
        .optimize = optimize,
    });

    // This creates another `std.Build.Step.Compile`, but this one builds an executable
    // rather than a static library.
    const exe = b.addExecutable(.{
        .name = "smp_debug_allocators",
        .root_module = exe_mod,
    });

    // This declares intent for the executable to be installed into the
    // standard location when the user invokes the "install" step (the default
    // step when running `zig build`).
    b.installArtifact(exe);

    // This *creates* a Run step in the build graph, to be executed when another
    // step is evaluated that depends on it. The next line below will establish
    // such a dependency.
    const run_cmd = b.addRunArtifact(exe);

    // By making the run step depend on the install step, it will be run from the
    // installation directory rather than directly from within the cache directory.
    // This is not necessary, however, if the application depends on other installed
    // files, this ensures they will be present and in the expected location.
    run_cmd.step.dependOn(b.getInstallStep());

    // This allows the user to pass arguments to the application in the build
    // command itself, like this: `zig build run -- arg1 arg2 etc`
    if (b.args) |args| {
        run_cmd.addArgs(args);
    }

    // This creates a build step. It will be visible in the `zig build --help` menu,
    // and can be selected like this: `zig build run`
    // This will evaluate the `run` step rather than the default, which is "install".
    const run_step = b.step("run", "Run the app");
    run_step.dependOn(&run_cmd.step);

    const exe_unit_tests = b.addTest(.{
        .root_module = exe_mod,
    });

    const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);

    // Similar to creating the run step earlier, this exposes a `test` step to
    // the `zig build --help` menu, providing a way for the user to request
    // running the unit tests.
    const test_step = b.step("test", "Run unit tests");
    test_step.dependOn(&run_exe_unit_tests.step);
}

build.zig.zon

.{
    // This is the default name used by packages depending on this one. For
    // example, when a user runs `zig fetch --save <url>`, this field is used
    // as the key in the `dependencies` table. Although the user can choose a
    // different name, most users will stick with this provided value.
    //
    // It is redundant to include "zig" in this name because it is already
    // within the Zig package namespace.
    .name = .smp_debug_allocators,

    // This is a [Semantic Version](https://semver.org/).
    // In a future version of Zig it will be used for package deduplication.
    .version = "0.0.0",

    // Together with name, this represents a globally unique package
    // identifier. This field is generated by the Zig toolchain when the
    // package is first created, and then *never changes*. This allows
    // unambiguous detection of one package being an updated version of
    // another.
    //
    // When forking a Zig project, this id should be regenerated (delete the
    // field and run `zig build`) if the upstream project is still maintained.
    // Otherwise, the fork is *hostile*, attempting to take control over the
    // original project's identity. Thus it is recommended to leave the comment
    // on the following line intact, so that it shows up in code reviews that
    // modify the field.
    .fingerprint = 0xb0e0f95d9406a205, // Changing this has security and trust implications.

    // Tracks the earliest Zig version that the package considers to be a
    // supported use case.
    .minimum_zig_version = "0.15.1",

    // This field is optional.
    // Each dependency must either provide a `url` and `hash`, or a `path`.
    // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
    // Once all dependencies are fetched, `zig build` no longer requires
    // internet connectivity.
    .dependencies = .{
        // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
        //.example = .{
        //    // When updating this field to a new URL, be sure to delete the corresponding
        //    // `hash`, otherwise you are communicating that you expect to find the old hash at
        //    // the new URL. If the contents of a URL change this will result in a hash mismatch
        //    // which will prevent zig from using it.
        //    .url = "https://example.com/foo.tar.gz",
        //
        //    // This is computed from the file contents of the directory of files that is
        //    // obtained after fetching `url` and applying the inclusion rules given by
        //    // `paths`.
        //    //
        //    // This field is the source of truth; packages do not come from a `url`; they
        //    // come from a `hash`. `url` is just one of many possible mirrors for how to
        //    // obtain a package matching this `hash`.
        //    //
        //    // Uses the [multihash](https://multiformats.io/multihash/) format.
        //    .hash = "...",
        //
        //    // When this is provided, the package is found in a directory relative to the
        //    // build root. In this case the package's hash is irrelevant and therefore not
        //    // computed. This field and `url` are mutually exclusive.
        //    .path = "foo",
        //
        //    // When this is set to `true`, a package is declared to be lazily
        //    // fetched. This makes the dependency only get fetched if it is
        //    // actually used.
        //    .lazy = false,
        //},
    },

    // Specifies the set of files and directories that are included in this package.
    // Only files and directories listed here are included in the `hash` that
    // is computed for this package. Only files listed here will remain on disk
    // when using the zig package manager. As a rule of thumb, one should list
    // files required for compilation plus any license(s).
    // Paths are relative to the build root. Use the empty string (`""`) to refer to
    // the build root itself.
    // A directory listed here means that all files within, recursively, are included.
    .paths = .{
        "build.zig",
        "build.zig.zon",
        "src",
        // For example...
        //"LICENSE",
        //"README.md",
    },
}

main.zig

const builtin = @import("builtin");
const std = @import("std");

fn alloc_test(allocator: std.mem.Allocator) !void {
    const magic_number = try allocator.create(i32);

    defer allocator.destroy(magic_number);

    magic_number.* = 42;

    std.debug.print("The magic number is {d}!\n", .{magic_number.*});
}

pub fn main() !void {
    var writer_buffer: [256]u8 = undefined;
    var writer = std.fs.File.stdout().writer(&writer_buffer);

    try writer.interface.print("All your {s} are belong to us.\n", .{"codebase"});

    try writer.interface.flush();

    var debug_allocator: std.heap.DebugAllocator(.{}) = .init;

    defer switch (builtin.mode) {
        .Debug => std.debug.assert(debug_allocator.deinit() == .ok),
        .ReleaseFast, .ReleaseSmall, .ReleaseSafe => {
            // Nothing
        },
    };

    const allocator = switch (builtin.mode) {
        .Debug => debug_allocator.allocator(),
        .ReleaseFast, .ReleaseSmall, .ReleaseSafe => std.heap.smp_allocator,
    };

    try alloc_test(allocator);
}