zig

name

zig

description

Up-to-date Zig programming language patterns for version 0.16.0. Use when writing, reviewing, or debugging Zig code, working with build.zig and build.zig.zon files, or using comptime metaprogramming. Critical for avoiding outdated patterns from training data - especially build system APIs (root_module instead of root_source_file), I/O APIs (buffered writer pattern), container initialization (.empty/.init), allocator selection (DebugAllocator), and removed language features (@Type, @cImport, async/await, usingnamespace).

Zig Language Reference (v0.16.0)

Zig evolves rapidly. Training data contains outdated patterns that cause compilation errors. This skill documents breaking changes and correct modern patterns.

Critical: 0.16.0 Breaking Changes

@Type - REMOVED

Replaced with individual type-creating builtins.

// WRONG - removed builtin
const T = @Type(.{ .int = .{ .signedness = .unsigned, .bits = 10 } });

// CORRECT
const T = @Int(.unsigned, 10);
const E = @Enum(.{ .tag_type = u8, .fields = &.{...}, .decls = &.{...}, .is_exhaustive = true });
const S = @Struct(.{ .layout = .auto, .fields = &.{...}, .decls = &.{...}, .is_tuple = false });
const U = @Union(.{ .layout = .auto, .tag_mode = .enum, .fields = &.{...}, .decls = &.{...} });
const P = @Pointer(.{ .size = .One, .is_const = false, .child = u8 });
const F = @Fn(.{ .calling_convention = .Unspecified, .is_var_args = false, .return_type = void, .params = &.{...} });
const L = @EnumLiteral("name"); // or just .name in most contexts

@cImport - DEPRECATED

C translation now happens in the build system. @cImport and @cInclude are deprecated.

// WRONG - deprecated
pub const c = @cImport({
    @cInclude("stdio.h");
});

// CORRECT - use addTranslateC in build.zig
const c_translate = b.addTranslateC(.{
    .root_source_file = b.path("src/c.h"),
    .target = target,
    .optimize = optimize,
});
exe.root_module.addImport("c", c_translate.createModule());

@intFromFloat - DEPRECATED

@floor, @ceil, @round, @trunc now convert floats directly to integers.

// WRONG - deprecated
const n: u8 = @intFromFloat(@floor(value));

// CORRECT
const n: u8 = @floor(value);
const m: i32 = @round(value);

Runtime Vector Indexing - REMOVED

Vector indexing with runtime indices is no longer allowed. Coerce to array first.

// WRONG - compile error
_ = vector[i];

// CORRECT
const array: [vector_type.len]vector_type.child = vector;
for (&array) |elem| { _ = elem; }

Returning Address of Local Variable - REMOVED

Returning &x where x is a local variable is now a compile error.

// WRONG - "returning address of expired local variable"
fn getX() *i32 {
    var x: i32 = 5;
    return &x;
}

// CORRECT - allocate on heap or use static storage

Pointers in Packed Structs/Unions - REMOVED

Pointer fields are no longer allowed in packed struct or packed union.

// WRONG
const S = packed struct { ptr: *u8 };

// CORRECT - use usize and convert with @ptrFromInt/@intFromPtr
const S = packed struct { ptr: usize };

Vectors and Arrays No Longer Support In-Memory Coercion

Use direct coercion instead of @ptrCast between array and vector memory.

Extern Contexts Require Explicit Backing Types

enum, packed struct, and packed union with inferred backing types are invalid in extern contexts.

// WRONG
const E = enum { a, b };
export var e: E = .a;

// CORRECT
const E = enum(u8) { a, b };
export var e: E = .a;

Packed Union Field Size Constraints

All fields of a packed union must have the same @bitSizeOf as the backing integer. Use explicit backing integer packed union(T) and padding structs where needed.

// WRONG
const U = packed union { x: u8, y: u16 };

// CORRECT
const U = packed union(u16) {
    x: packed struct(u16) { data: u8, padding: u8 = 0 },
    y: u16,
};

Critical: Removed Features (0.15.x)

usingnamespace - REMOVED

// WRONG - compile error
pub usingnamespace @import("other.zig");

// CORRECT - explicit re-export
const other = @import("other.zig");
pub const foo = other.foo;

async/await - REMOVED

Keywords removed from language. Replaced with the std.Io concurrency model in 0.16.0.

Critical: I/O as an Interface (0.16.0)

All I/O functionality now requires an explicit Io instance. Anything that blocks control flow or introduces nondeterminism is owned by the I/O interface.

"Juicy Main"

Main functions now receive initialization state via std.process.Init:

// WRONG - old main signature
pub fn main() !void {
    const gpa = std.heap.DebugAllocator(.{}).init;
    // ...
}

// CORRECT - new "Juicy Main"
pub fn main(init: std.process.Init) !void {
    const gpa = init.gpa;
    const io = init.io;
    const args = try init.minimal.args.toSlice(init.arena.allocator());
    // ...
}

When upgrading without an Io instance:

var threaded: Io.Threaded = .init_single_threaded;
const io = threaded.io();
// Non-ideal workaround; prefer accepting Io as a parameter

⚠️ io parameter type: use anytype, not Io.Threaded

init.io returns the generic Io interface type, NOT Io.Threaded. Functions that accept an io parameter should use anytype:

// WRONG — "expected type 'Io.Threaded', found 'Io'"
fn train(io: std.Io.Threaded) !void { ... }

// CORRECT
fn train(io: anytype) !void { ... }

pub fn main(init: std.process.Init) !void {
    const io = init.io;  // io is generic Io interface
    try train(io);       // passes cleanly with anytype
}

The Io variants (Threaded, Evented, failing) are implementations, not interchangeable with the generic interface type.

Io Implementations

• Io.Threaded — stable, well-tested. Direct blocking syscalls on threads.
  • -fno-single-threaded — supports task-level concurrency and cancelation.
  • -fsingle-threaded — sequential execution.
• Io.Evented — experimental M:N threading / stackful coroutines.
  • Backends: Io.Uring (Linux io_uring, incomplete), Io.Kqueue, Io.Dispatch (GCD/macOS).
• Io.failing — simulates a system with no operations.

Concurrency: Future, Group, Batch

io.async creates an independent task; io.concurrent creates one that must run concurrently (can fail with error.ConcurrencyUnavailable). Both return a Future(T) with .await and .cancel.

var task = io.async(downloadFile, .{ io, url });
defer if (task.cancel(io)) |file| file.close(io) else |_| {}
const result = try task.await(io);

Group manages many tasks with the same lifetime (O(1) spawn overhead):

var group: Io.Group = .init;
defer group.cancel(io);
for (urls) |url| group.async(io, fetch, .{ io, url });
try group.await(io);

Batch is a lower-level abstraction for concurrent operations (currently FileReadStreaming, FileWriteStreaming, DeviceIoControl, NetReceive). More efficient than Future but less flexible.

Cancelation

All cancelable I/O operations include error.Canceled in their error sets. Requesting cancelation is equivalent to awaiting plus an interrupt request. Handle it by propagating, calling io.recancel(), or using io.swapCancelProtection(). Add explicit cancelation points in long CPU tasks with io.checkCancel().

Sync Primitives Migrated to std.Io

Old (0.15.x)	New (0.16.0)
std.Thread.ResetEvent	std.Io.Event
std.Thread.WaitGroup	std.Io.Group
std.Thread.Futex	std.Io.Futex
std.Thread.Mutex	std.Io.Mutex
std.Thread.Condition	std.Io.Condition
std.Thread.Semaphore	std.Io.Semaphore
std.Thread.RwLock	std.Io.RwLock
std.once	REMOVED — avoid globals or hand-roll

Lock-free primitives do not require std.Io integration.

Entropy / Random

// WRONG - old API
std.crypto.random.bytes(&buffer);
const rng = std.crypto.random;

// CORRECT
io.random(&buffer);
const rng_impl: std.Random.IoSource = .{ .io = io };
const rng = rng_impl.interface();
// Use `io.randomSecure(&buffer)` for CSPRNG without in-process state

Time

// WRONG - old API
const now = std.time.timestamp;
const instant = std.time.Instant.now();

// CORRECT
const ts = std.Io.Timestamp.now(io);
const clock = std.Io.Clock.monotonic;
const resolution = try clock.resolution(io);

File System (std.fs → std.Io)

All filesystem APIs migrated to std.Io.

// WRONG - old API
const file = try std.fs.cwd().openFile("foo.txt", .{});
defer file.close();
try file.writeAll("hello");

// CORRECT
const file = try std.Io.Dir.cwd().openFile(io, "foo.txt", .{});
defer file.close(io);
try file.writeStreamingAll(io, "hello");

Major renames:

• std.fs.Dir → std.Io.Dir
• std.fs.File → std.Io.File
• fs.Dir.makeDir → Io.Dir.createDir
• fs.File.read → Io.File.readStreaming
• fs.File.write → Io.File.writeStreaming
• fs.File.pread → Io.File.readPositional
• fs.File.pwrite → Io.File.writePositional
• fs.File.getEndPos → Io.File.length
• fs.File.setEndPos → Io.File.setLength
• fs.File.chmod → Io.File.setPermissions
• fs.selfExePath → std.process.executablePath
• fs.openSelfExe → std.process.openExecutable

See full migration list in the 0.16.0 release notes.

Networking (std.net / std.http → std.Io)

All networking APIs now require Io. Io.Evented does not yet implement networking.

const host_name: Io.net.HostName = try .init(args[1]);
var http_client: std.http.Client = .{ .allocator = gpa, .io = io };
var request = try http_client.request(.HEAD, .{ .host = .{ .percent_encoded = host_name.bytes } }, .{});
try request.sendBodiless();

Process

// WRONG - old API
var child = std.process.Child.init(argv, gpa);
try child.spawn(io);
const result = try std.process.Child.run(allocator, io, .{ ... });

// CORRECT
var child = try std.process.spawn(io, .{ .argv = argv, .stdin = .pipe, .stdout = .pipe });
const result = try std.process.run(allocator, io, .{ ... });

// Replace current process image
const err = std.process.replace(io, .{ .argv = argv });

Environment Variables

std.process.getEnvVarOwned / getEnvMap / hasEnvVar are REMOVED. The environment now arrives through the main function's Init parameter — there is no global accessor, so a function that needs env vars must be passed the map.

// WRONG - removed
const val = try std.process.getEnvVarOwned(gpa, "OSS_AK");
var env = try std.process.getEnvMap(gpa);

// CORRECT - via Init (no allocation, no free; borrowed from the map)
pub fn main(init: std.process.Init) !void {
    const val = init.environ_map.get("OSS_AK") orelse return error.MissingVar;
    // `Init.Minimal` variant exposes `init.minimal.environ` instead
}

Init.environ_map is a *Environ.Map and is documented not threadsafe — read what you need up front rather than calling .get() from worker threads.

posix and os.windows Removals

Most std.posix and std.os.windows medium-level functions removed. Choose:

• Higher: use std.Io
• Lower: use std.posix.system directly

Critical: I/O API Rewrite ("Writergate")

The entire std.io API changed. New std.Io.Writer and std.Io.Reader are non-generic with buffer in the interface.

Writing

// WRONG - old API
const stdout = std.io.getStdOut().writer();
try stdout.print("Hello\n", .{});

// CORRECT - new API: provide Io, buffer, access .interface, flush
var buf: [4096]u8 = undefined;
var file_writer = std.Io.File.stdout().writer(io, &buf);
const stdout = &file_writer.interface;
try stdout.print("Hello\n", .{});
try stdout.flush();  // REQUIRED!

CRITICAL: print() always requires args tuple. Even format strings without specifiers need , .{}:

// WRONG — "expected 2 argument(s), found 1"
try w.print("hello\n");

// CORRECT
try w.print("hello\n", .{});
try w.print("count = {d}\n", .{42});

File.Writer vs Io.Writer are different types. Use .interface to bridge:

var fw = file.writer(io, &buf);  // returns std.Io.File.Writer
const w = &fw.interface;          // *std.Io.Writer — the type functions expect

Format specifiers for f64: {d} formats f64 as decimal float (NOT {f} or {g}):

• {d} — decimal float (calls printFloat internally)
• {f} — calls value.format(w) (custom format method — different semantic!)
• {g} — NOT supported for f64 (compile error)
• {e} — scientific notation
• Precision works with {d:>4.1} (width 4, precision 1, right-aligned)

Reading

// Reading from file
var buf: [4096]u8 = undefined;
var file_reader = file.reader(&buf);
const r = &file_reader.interface;

// Read line by line (takeDelimiter returns null at EOF)
while (try r.takeDelimiter('\n')) |line| {
    // process line (doesn't include '\n')
}

// Read binary data
const header = try r.takeStruct(Header, .little);
const value = try r.takeInt(u32, .big);

Fixed Buffer Writer (no file)

var buf: [256]u8 = undefined;
var w: std.Io.Writer = .fixed(&buf);
try w.print("Hello {s}", .{"world"});
const result = w.buffered();  // "Hello world"

Fixed Reader (from slice)

var r: std.Io.Reader = .fixed("hello\nworld");
const line = (try r.takeDelimiter('\n')).?;  // "hello" (returns null at EOF)

Deprecated: BufferedWriter, CountingWriter, std.io.bufferedWriter()

Deprecated: GenericWriter, GenericReader, AnyWriter, AnyReader, FixedBufferStream

New: std.Io.Writer, std.Io.Reader - non-generic, buffer in interface

Replacements:

• CountingWriter → std.Io.Writer.Discarding (has .fullCount())
• BufferedWriter → buffer provided to .writer(&buf) call
• Allocating output → std.Io.Writer.Allocating

build.zig.zon (ZON Format)

ZON (Zig Object Notation) in build.zig.zon has specific syntax rules.

.name is an enum literal, not a string

// WRONG - "expected enum literal"
.name = "my_package",

// CORRECT
.name = .my_package,

.fingerprint is required

.fingerprint = 0x7dab62f80910e47b,
// If new project, use the fingerprint value the compiler suggests

See std.zon for complete ZON format reference.

Critical: Build System (0.15.x)

root_source_file is REMOVED from addExecutable/addLibrary/addTest. Use root_module:

// WRONG - removed field
b.addExecutable(.{
    .name = "app",
    .root_source_file = b.path("src/main.zig"),  // ERROR
    .target = target,
});

// CORRECT
b.addExecutable(.{
    .name = "app",
    .root_module = b.createModule(.{
        .root_source_file = b.path("src/main.zig"),
        .target = target,
        .optimize = optimize,
    }),
});

Module imports changed:

// WRONG (old API)
exe.addModule("helper", helper_mod);

// CORRECT
exe.root_module.addImport("helper", helper_mod);

Adding dependency modules:

const dep = b.dependency("lib", .{ .target = target, .optimize = optimize });
exe.root_module.addImport("lib", dep.module("lib"));

Compile-level methods deprecated: exe.linkSystemLibrary(), exe.addCSourceFiles(), exe.addIncludePath(), exe.linkLibC() are deprecated — use exe.root_module.* equivalents instead.

See std.Build reference for complete build system documentation.

Critical: Container Initialization

Never use .{} for containers. Use .empty or .init:

// WRONG - deprecated
var list: std.ArrayList(u32) = .{};
var gpa: std.heap.DebugAllocator(.{}) = .{};

// CORRECT - use .empty for empty collections
var list: std.ArrayList(u32) = .empty;
var map: std.AutoHashMapUnmanaged(u32, u32) = .empty;

// CORRECT - use .init for stateful types with internal config
var gpa: std.heap.DebugAllocator(.{}) = .init;
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);

Naming Changes

• std.ArrayListUnmanaged → std.ArrayList (Unmanaged is now default, old name deprecated)
• std.heap.GeneralPurposeAllocator → std.heap.DebugAllocator (GPA alias still works)

std.BoundedArray - REMOVED. Use:

var buffer: [8]i32 = undefined;
var stack = std.ArrayList(i32).initBuffer(&buffer);

Critical: Format Strings (0.15.x)

{f} required to call format methods:

// WRONG - ambiguous error
std.debug.print("{}", .{std.zig.fmtId("x")});

// CORRECT
std.debug.print("{f}", .{std.zig.fmtId("x")});

Format method signature changed:

// OLD - wrong
pub fn format(self: @This(), comptime fmt: []const u8, opts: std.fmt.FormatOptions, writer: anytype) !void

// NEW - correct
pub fn format(self: @This(), writer: *std.Io.Writer) std.Io.Writer.Error!void

Breaking Changes (0.14.0+)

@branchHint replaces @setCold

// WRONG
@setCold(true);

// CORRECT
@branchHint(.cold);  // Must be first statement in block

@export takes pointer

// WRONG
@export(foo, .{ .name = "bar" });

// CORRECT
@export(&foo, .{ .name = "bar" });

Inline asm clobbers are typed

// WRONG
: "rcx", "r11"

// CORRECT
: .{ .rcx = true, .r11 = true }

@fence - REMOVED

Use stronger atomic orderings or RMW operations instead.

Decl Literals (0.14.0+)

.identifier syntax works for declarations:

const S = struct {
    x: u32,
    const default: S = .{ .x = 0 };
    fn init(v: u32) S { return .{ .x = v }; }
};

const a: S = .default;      // S.default
const b: S = .init(42);     // S.init(42)
const c: S = try .init(1);  // works with try

Labeled Switch (0.14.0+)

State machines use continue :label:

state: switch (initial) {
    .idle => continue :state .running,
    .running => if (done) break :state result else continue :state .running,
    .error => return error.Failed,
}

Non-exhaustive Enum Switch (0.15.x)

Can mix explicit tags with _ and else:

switch (value) {
    .a, .b => {},
    else => {},  // other named tags
    _ => {},     // unnamed integer values
}

0.16.0 Additive Changes

Switch Enhancements

packed struct and packed union can now be used as switch prongs. Decl literals and @enumFromInt work in prongs. Union tag captures allowed for all prongs. Captures may no longer all be discarded.

Small Integers Coerce to Floats

Integers that fit exactly in a float's significand coerce implicitly.

var f: f32 = foo_int; // u24 coerces safely; u25 still needs @floatFromInt

Unary Float Builtins Forward Result Type

@sqrt, @sin, @cos, @tan, @exp, @exp2, @log, @log2, @log10, @floor, @ceil, @trunc, @round now forward result type.

const x: f64 = @sqrt(@floatFromInt(N)); // now works directly

Explicit Backing Integers on Packed Unions

packed union(T) syntax now supported, matching packed struct(T).

const Split16 = packed union(u16) { raw: MaybeSigned16, split: packed struct { low: u8, high: u8 } };

Explicitly-Aligned Pointer Types Are Distinct

*u8 and *align(1) u8 are now distinct types, though they still coerce to each other.

Lazy Field Analysis

Structs, unions, enums, and opaques are only resolved when size or field type is required. Using types as namespaces no longer pulls in unused fields.

Pointers to Comptime-Only Types Are Runtime Types

*comptime_int and []comptime_int are now runtime types (though dereferencing remains comptime-only).

Quick Fixes

Error	Fix
@Type was removed from the language	Use @Int, @Enum, @Struct, @Union, @Pointer, @Fn, @Tuple, @EnumLiteral
@cImport is deprecated	Use b.addTranslateC() in build.zig
@intFromFloat is deprecated	Use @floor, @ceil, @round, or @trunc directly to integer
runtime index into vector type	Coerce vector to array first: const arr: [N]T = vector;
returning address of expired local variable	Return by value, use heap allocation, or use static storage
packed structs and unions cannot contain pointers	Use usize with @ptrFromInt/@intFromPtr
no field 'root_source_file'	Use root_module = b.createModule(.{...})
use of undefined value	Arithmetic on undefined is now illegal
type 'f32' cannot represent integer	Use float literal: 123_456_789.0 not 123_456_789
ambiguous format string	Use {f} for format methods
sanitize_c = true	Type changed to ?std.zig.SanitizeC — use .full, .trap, or .off
std.fifo.LinearFifo	Removed — use std.Io.Reader/Writer patterns
posix.sendfile	Removed — use std.Io.File writer

Language References

Load these references when working with core language features:

Code Style

• Style Guide - Official Zig naming conventions (TitleCase types, camelCase functions, snake_case variables), whitespace rules, doc comment guidance, redundancy avoidance, zig fmt

Language Basics & Built-ins

• Language Basics - Core language: types, control flow (if/while/for/switch), error handling (try/catch/errdefer), optionals, structs, enums, unions, pointers, slices, comptime, functions
• Built-in Functions - All @ built-ins: type casts (@intCast, @bitCast, @ptrCast), arithmetic (@addWithOverflow, @divExact), bit ops (@clz, @popCount), memory (@memcpy, @sizeOf), atomics (@atomicRmw, @cmpxchgWeak), introspection (@typeInfo, @TypeOf, @hasDecl, @Int, @Struct, @Union, @Enum), SIMD (@Vector, @splat, @reduce), C interop (@export, addTranslateC in build system)

Standard Library References

Load these references when working with specific modules:

Memory & Slices

• std.mem - Slice search/compare, split/tokenize, alignment, endianness, byte conversion

Text & Encoding

• std.fmt - Format strings, integer/float parsing, hex encoding, custom formatters, {f} specifier (0.15.x)
• std.ascii - ASCII character classification (isAlpha, isDigit), case conversion, case-insensitive comparison
• std.unicode - UTF-8/UTF-16 encoding/decoding, codepoint iteration, validation, WTF-8 for Windows
• std.base64 - Base64 encoding/decoding (standard, URL-safe, with/without padding)

Math & Random

• std.math - Floating-point ops, trig, overflow-checked arithmetic, constants, complex numbers, big integers
• std.Random - PRNGs (Xoshiro256, Pcg), CSPRNGs (ChaCha), random integers/floats/booleans, shuffle, distributions
• std.hash - Non-cryptographic hash functions (Wyhash, XxHash, FNV, Murmur, CityHash), checksums (CRC32, Adler32), auto-hashing

SIMD & Vectorization

• std.simd - SIMD vector utilities: optimal vector length, iota/repeat/join/interlace patterns, element shifting/rotation, parallel searching, prefix scans, branchless selection

Time & Timing

• std.time - Wall-clock timestamps, monotonic Instant/Timer, epoch conversions, calendar utilities (year/month/day), time unit constants
• std.Tz - TZif timezone database parsing (RFC 8536), UTC offsets, DST rules, timezone abbreviations, leap seconds

Sorting & Searching

• std.sort - Sorting algorithms (pdq, block, heap, insertion), binary search, min/max

Core Data Structures

• std.ArrayList - Dynamic arrays, vectors, BoundedArray replacement
• std.HashMap / AutoHashMap - Hash maps, string maps, ordered maps
• std.ArrayHashMap - Insertion-order preserving hash map, array-style key/value access
• std.MultiArrayList - Struct-of-arrays for cache-efficient struct storage
• std.SegmentedList - Stable pointers, arena-friendly, non-copyable types
• std.DoublyLinkedList / SinglyLinkedList - Intrusive linked lists, O(1) insert/remove
• std.PriorityQueue - Binary heap, min/max extraction, task scheduling
• std.PriorityDequeue - Min-max heap, double-ended priority extraction
• std.Treap - Self-balancing BST, ordered keys, min/max/predecessor
• std.bit_set - Bit sets (Static, Dynamic, Integer, Array), set operations, iteration
• std.BufMap / BufSet - String-owning maps and sets, automatic key/value memory management
• std.StaticStringMap - Compile-time optimized string lookup, perfect hash for keywords
• std.enums - EnumSet, EnumMap, EnumArray: bit-backed enum collections

Allocators

• std.heap - Allocator selection guide, ArenaAllocator, DebugAllocator, FixedBufferAllocator, MemoryPool, SmpAllocator, ThreadSafeAllocator, StackFallbackAllocator, custom allocator implementation

I/O & Files

• std.io - Reader/Writer API (0.15.x): buffered I/O, streaming, binary data, format strings
• std.fs - File system: files, directories, iteration, atomic writes, paths
• std.tar - Tar archive reading/writing, extraction, POSIX ustar, GNU/pax extensions
• std.zip - ZIP archive reading/extraction, ZIP64 support, store/deflate compression
• std.compress - Compression: DEFLATE (gzip, zlib), Zstandard, LZMA, LZMA2, XZ decompression/compression

Networking

• std.http - HTTP client/server, TLS, connection pooling, compression, WebSocket
• std.net - TCP/UDP sockets, address parsing, DNS resolution
• std.Uri - URI parsing/formatting (RFC 3986), percent-encoding/decoding, relative URI resolution

Process Management

• std.process - Child process spawning, environment variables, argument parsing, exec

OS-Specific APIs

• std.os - OS-specific APIs: Linux syscalls, io_uring, Windows NT APIs, WASI, direct platform access
• std.c - C ABI types and libc bindings: platform-specific types (fd_t, pid_t, timespec), errno values, socket/signal/memory types, fcntl/open flags, FFI with C libraries

Concurrency

• std.Thread - Thread spawning, Mutex, RwLock, Condition, Semaphore, WaitGroup, thread pools
• std.atomic - Lock-free atomic operations: Value wrapper, fetch-and-modify (add/sub/and/or/xor), compare-and-swap, atomic ordering semantics, spin loop hints, cache line sizing

Patterns & Best Practices

• Zig Patterns - Load when writing new code or reviewing code quality. Comprehensive best practices extracted from the Zig standard library: quick patterns (memory/allocators, file I/O, HTTP, JSON, testing, build system) plus idiomatic code patterns covering syntax (closures, context pattern, options structs, destructuring), polymorphism (duck typing, generics, custom formatting, dynamic/static dispatch), safety (diagnostics, error payloads, defer/errdefer, compile-time assertions), and performance (const pointer passing)
• Code Review - Load when reviewing Zig code. Systematic checklist organized by confidence level: ALWAYS FLAG (removed features, changed syntax, API changes), FLAG WITH CONTEXT (exception safety bugs, missing flush, allocator issues), SUGGEST (style improvements). Includes migration examples for 0.14/0.15 breaking changes

Serialization

• std.json - JSON parsing, serialization, dynamic values, streaming, custom parse/stringify
• std.zon - ZON (Zig Object Notation) parsing and serialization for build.zig.zon, config files, data interchange

Testing & Debug

• std.testing - Unit test assertions and utilities
• std.debug - Panic, assert, stack traces, hex dump, format specifiers
• std.log - Scoped logging with configurable levels and output

Metaprogramming

• Comptime Reference - Comptime fundamentals, type reflection (@typeInfo/@Int/@Struct/@Union/@Enum/@TypeOf), loop variants (comptime for vs inline for), branch elimination, type generation, comptime limitations
• std.meta - Type introspection, field iteration, stringToEnum, generic programming

Compiler Utilities

• std.zig - AST parsing, tokenization, source analysis, linters, formatters, ZON parsing

Security & Cryptography

• std.crypto - Hashing (SHA2, SHA3, Blake3), AEAD (AES-GCM, ChaCha20-Poly1305), signatures (Ed25519, ECDSA), key exchange (X25519), password hashing (Argon2, scrypt, bcrypt), secure random, timing-safe operations

Namespace depth trips people up — MACs live under crypto.auth, not crypto directly, and hashes are grouped by family:

std.crypto.auth.hmac.HmacSha1          // NOT std.crypto.hmac.HmacSha1
std.crypto.auth.hmac.HmacMd5
std.crypto.auth.hmac.sha2.HmacSha256   // sha2 family is one level deeper
std.crypto.hash.Sha1                   // hashes: crypto.hash.*
std.crypto.hash.sha2.Sha256

HmacSha1 is the one to reach for when implementing AWS SigV1 / Aliyun OSS V1 signing. One-shot form: HmacSha1.create(&out, msg, key) with out: [HmacSha1.mac_length]u8.

Build System

• std.Build - Build system: build.zig, modules, dependencies, build.zig.zon, steps, options, testing, C/C++ integration

Interoperability

• C Interop - Exporting C-compatible APIs: export fn, C calling convention, building static/dynamic libraries, creating headers, macOS universal binaries, XCFramework for Swift/Xcode, module maps