zig-best-practices

name	zig-best-practices
description	Use when reading or writing Zig files (.zig, build.zig, build.zig.zon).

Zig Best Practices

Follows type-first, functional, and error handling patterns from AGENTS.md. This skill covers Zig-specific idioms only.

Type System Patterns

Tagged unions for mutually exclusive states — prevents invalid combinations that a struct with multiple nullable fields would allow:

const RequestState = union(enum) {
    idle,
    loading,
    success: []const u8,
    failure: anyerror,
};

Explicit error sets — documents exactly what can fail; anyerror hides failure modes:

const ParseError = error{ InvalidSyntax, UnexpectedToken, EndOfInput };
fn parse(input: []const u8) ParseError!Ast { ... }

Distinct types for domain IDs — compiler prevents mixing up different ID types:

const UserId = enum(u64) { _ };
const OrderId = enum(u64) { _ };

Comptime validation — catch invalid configurations at compile time, not runtime:

fn Buffer(comptime size: usize) type {
    if (size == 0) @compileError("buffer size must be greater than 0");
    return struct { data: [size]u8 = undefined, len: usize = 0 };
}

Memory Management

• Pass allocators explicitly to every function that allocates; no global allocator state.
• Place defer resource.deinit() immediately after acquisition — keeps cleanup co-located with creation.
• Use errdefer for cleanup on error paths; defer for unconditional cleanup.
• Use arena allocators for batch/temporary work; they free everything at once.
• Use std.testing.allocator in tests — reports leaks with stack traces.

fn createResource(allocator: std.mem.Allocator) !*Resource {
    const resource = try allocator.create(Resource);
    errdefer allocator.destroy(resource);  // runs only on error
    resource.* = try initializeResource();
    return resource;
}

Safety Idioms

Runs on the assertions-and-bounds law from AGENTS.md; these are the Zig-specific levers.

• std.debug.assert for invariants; comptime asserts check design relationships between constants (type sizes, layout invariants) before the program even runs.
• Prefer explicitly-sized integers (u32, u64) where the domain owns the type; keep usize at the std-lib seam (slice lengths, indices) instead of propagating it inward through @intCast chains.
• Decide allocation up front: arenas or fixed buffers sized at init for the data plane; every long-lived cache or pool carries an explicit upper bound.
• Construct large structs in place via an out-pointer (fn init(target: *T) !void) for pointer stability and no intermediate copy-moves; in-place init is viral — if a field needs it, the container does too.

Key Conventions

• Prefer const over var; prefer slices over raw pointers.
• Prefer comptime T: type over anytype; explicit types produce clearer errors. Use anytype only for genuinely polymorphic cases (callbacks, std.debug.print-style).
• Exhaustive switch: include an else returning an error or unreachable for truly impossible cases.
• Use std.log.scoped(.module_name) for namespaced logging; define a module-level const log constant.
• Larger cohesive files are idiomatic — tests alongside implementation, comptime generics at file scope.

Advanced Topics

• Generic containers (queues, stacks, trees): See GENERICS.md
• C library interop (raylib, SDL, curl): See C-INTEROP.md
• Debugging memory leaks (GPA, stack traces): See DEBUGGING.md

Tooling

zigdoc — browse std library and dependency docs:

zigdoc std.mem.Allocator   # std lib symbol
zigdoc vaxis.Window        # project dependency
zigdoc @init               # create AGENTS.md with API patterns

ziglint — static analysis with .ziglint.zon config:

ziglint                    # lint current directory
ziglint --ignore Z001      # suppress specific rule

References

• Language Reference: https://ziglang.org/documentation/0.15.2/
• Standard Library: https://ziglang.org/documentation/0.15.2/std/
• Zig Guide: https://zig.guide/