Zig Best Practices Type-First Development
Types define the contract before implementation. Follow this workflow:
Define data structures - structs, unions, and error sets first Define function signatures - parameters, return types, and error unions Implement to satisfy types - let the compiler guide completeness Validate at comptime - catch invalid configurations during compilation Make Illegal States Unrepresentable
Use Zig's type system to prevent invalid states at compile time.
Tagged unions for mutually exclusive states:
// Good: only valid combinations possible const RequestState = union(enum) { idle, loading, success: []const u8, failure: anyerror, };
fn handleState(state: RequestState) void { switch (state) { .idle => {}, .loading => showSpinner(), .success => |data| render(data), .failure => |err| showError(err), } }
// Bad: allows invalid combinations const RequestState = struct { loading: bool, data: ?[]const u8, err: ?anyerror, };
Explicit error sets for failure modes:
// Good: documents exactly what can fail const ParseError = error{ InvalidSyntax, UnexpectedToken, EndOfInput, };
fn parse(input: []const u8) ParseError!Ast { // implementation }
// Bad: anyerror hides failure modes fn parse(input: []const u8) anyerror!Ast { // implementation }
Distinct types for domain concepts:
// Prevent mixing up IDs of different types const UserId = enum(u64) { _ }; const OrderId = enum(u64) { _ };
fn getUser(id: UserId) !User { // Compiler prevents passing OrderId here }
fn createUserId(raw: u64) UserId { return @enumFromInt(raw); }
Comptime validation for invariants:
fn Buffer(comptime size: usize) type { if (size == 0) { @compileError("buffer size must be greater than 0"); } if (size > 1024 * 1024) { @compileError("buffer size exceeds 1MB limit"); } return struct { data: [size]u8 = undefined, len: usize = 0, }; }
Non-exhaustive enums for extensibility:
// External enum that may gain variants const Status = enum(u8) { active = 1, inactive = 2, pending = 3, _, };
fn processStatus(status: Status) !void { switch (status) { .active => {}, .inactive => {}, .pending => {}, _ => return error.UnknownStatus, } }
Module Structure
Larger cohesive files are idiomatic in Zig. Keep related code together: tests alongside implementation, comptime generics at file scope, public/private controlled by pub. Split only when a file handles genuinely separate concerns. The standard library demonstrates this pattern with files like std/mem.zig containing 2000+ lines of cohesive memory operations.
Instructions Return errors with context using error unions (!T); every function returns a value or an error. Explicit error sets document failure modes. Use errdefer for cleanup on error paths; use defer for unconditional cleanup. This prevents resource leaks without try-finally boilerplate. Handle all branches in switch statements; include an else clause that returns an error or uses unreachable for truly impossible cases. Pass allocators explicitly to functions requiring dynamic memory; prefer std.testing.allocator in tests for leak detection. Prefer const over var; prefer slices over raw pointers for bounds safety. Immutability signals intent and enables optimizations. Avoid anytype; prefer explicit comptime T: type parameters. Explicit types document intent and produce clearer error messages. Use std.log.scoped for namespaced logging; define a module-level log constant for consistent scope across the file. Add or update tests for new logic; use std.testing.allocator to catch memory leaks automatically. Examples
Explicit failure for unimplemented logic:
fn buildWidget(widget_type: []const u8) !Widget { return error.NotImplemented; }
Propagate errors with try:
fn readConfig(path: []const u8) !Config { const file = try std.fs.cwd().openFile(path, .{}); defer file.close(); const contents = try file.readToEndAlloc(allocator, max_size); return parseConfig(contents); }
Resource cleanup with errdefer:
fn createResource(allocator: std.mem.Allocator) !*Resource { const resource = try allocator.create(Resource); errdefer allocator.destroy(resource);
resource.* = try initializeResource();
return resource;
}
Exhaustive switch with explicit default:
fn processStatus(status: Status) ![]const u8 { return switch (status) { .active => "processing", .inactive => "skipped", _ => error.UnhandledStatus, }; }
Testing with memory leak detection:
const std = @import("std");
test "widget creation" { const allocator = std.testing.allocator; var list: std.ArrayListUnmanaged(u32) = .empty; defer list.deinit(allocator);
try list.append(allocator, 42);
try std.testing.expectEqual(1, list.items.len);
}
Memory Management Pass allocators explicitly; never use global state for allocation. Functions declare their allocation needs in parameters. Use defer immediately after acquiring a resource. Place cleanup logic next to acquisition for clarity. Prefer arena allocators for temporary allocations; they free everything at once when the arena is destroyed. Use std.testing.allocator in tests; it reports leaks with stack traces showing allocation origins. Examples
Allocator as explicit parameter:
fn processData(allocator: std.mem.Allocator, input: []const u8) ![]u8 { const result = try allocator.alloc(u8, input.len * 2); errdefer allocator.free(result);
// process input into result
return result;
}
Arena allocator for batch operations:
fn processBatch(items: []const Item) !void { var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator); defer arena.deinit(); const allocator = arena.allocator();
for (items) |item| {
const processed = try processItem(allocator, item);
try outputResult(processed);
}
// All allocations freed when arena deinits
}
Logging Use std.log.scoped to create namespaced loggers; each module should define its own scoped logger for filtering. Define a module-level const log at the top of the file; use it consistently throughout the module. Use appropriate log levels: err for failures, warn for suspicious conditions, info for state changes, debug for tracing. Examples
Scoped logger for a module:
const std = @import("std"); const log = std.log.scoped(.widgets);
pub fn createWidget(name: []const u8) !Widget { log.debug("creating widget: {s}", .{name}); const widget = try allocateWidget(name); log.debug("created widget id={d}", .{widget.id}); return widget; }
pub fn deleteWidget(id: u32) void { log.info("deleting widget id={d}", .{id}); // cleanup }
Multiple scopes in a codebase:
// In src/db.zig const log = std.log.scoped(.db);
// In src/http.zig const log = std.log.scoped(.http);
// In src/auth.zig const log = std.log.scoped(.auth);
Comptime Patterns Use comptime parameters for generic functions; type information is available at compile time with zero runtime cost. Prefer compile-time validation over runtime checks when possible. Catch errors during compilation rather than in production. Use @compileError for invalid configurations that should fail the build. Examples
Generic function with comptime type:
fn max(comptime T: type, a: T, b: T) T { return if (a > b) a else b; }
Compile-time validation:
fn createBuffer(comptime size: usize) [size]u8 { if (size == 0) { @compileError("buffer size must be greater than 0"); } return [_]u8{0} ** size; }
Avoiding anytype Prefer comptime T: type over anytype; explicit type parameters document expected constraints and produce clearer errors. Use anytype only when the function genuinely accepts any type (like std.debug.print) or for callbacks/closures. When using anytype, add a doc comment describing the expected interface or constraints. Examples
Prefer explicit comptime type (good):
fn sum(comptime T: type, items: []const T) T { var total: T = 0; for (items) |item| { total += item; } return total; }
Avoid anytype when type is known (bad):
// Unclear what types are valid; error messages will be confusing fn sum(items: anytype) @TypeOf(items[0]) { // ... }
Acceptable anytype for callbacks:
/// Calls callback for each item. Callback must accept (T) and return void.
fn forEach(comptime T: type, items: []const T, callback: anytype) void {
for (items) |item| {
callback(item);
}
}
Using @TypeOf when anytype is necessary:
fn debugPrint(value: anytype) void { const T = @TypeOf(value); if (@typeInfo(T) == .Pointer) { std.debug.print("ptr: {*}\n", .{value}); } else { std.debug.print("val: {}\n", .{value}); } }
Error Handling Patterns Define specific error sets for functions; avoid anyerror when possible. Specific errors document failure modes. Use catch with a block for error recovery or logging; use catch unreachable only when errors are truly impossible. Merge error sets with || when combining operations that can fail in different ways. Examples
Specific error set:
const ConfigError = error{ FileNotFound, ParseError, InvalidFormat, };
fn loadConfig(path: []const u8) ConfigError!Config { // implementation }
Error handling with catch block:
const value = operation() catch |err| { std.log.err("operation failed: {}", .{err}); return error.OperationFailed; };
Configuration Load config from environment variables at startup; validate required values before use. Missing config should cause a clean exit with a descriptive message. Define a Config struct as single source of truth; avoid std.posix.getenv scattered throughout code. Use sensible defaults for development; require explicit values for production secrets. Examples
Typed config struct:
const std = @import("std");
pub const Config = struct { port: u16, database_url: []const u8, api_key: []const u8, env: []const u8, };
pub fn loadConfig() !Config { const db_url = std.posix.getenv("DATABASE_URL") orelse return error.MissingDatabaseUrl; const api_key = std.posix.getenv("API_KEY") orelse return error.MissingApiKey; const port_str = std.posix.getenv("PORT") orelse "3000"; const port = std.fmt.parseInt(u16, port_str, 10) catch return error.InvalidPort;
return .{
.port = port,
.database_url = db_url,
.api_key = api_key,
.env = std.posix.getenv("ENV") orelse "development",
};
}
Optionals Use orelse to provide default values for optionals; use .? only when null is a program error. Prefer if (optional) |value| pattern for safe unwrapping with access to the value. Examples
Safe optional handling:
fn findWidget(id: u32) ?*Widget { // lookup implementation }
fn processWidget(id: u32) !void { const widget = findWidget(id) orelse return error.WidgetNotFound; try widget.process(); }
Optional with if unwrapping:
if (maybeValue) |value| { try processValue(value); } else { std.log.warn("no value present", .{}); }
Advanced Topics
Reference these guides for specialized patterns:
Building custom containers (queues, stacks, trees): See GENERICS.md Interfacing with C libraries (raylib, SDL, curl, system APIs): See C-INTEROP.md Debugging memory leaks (GPA, stack traces): See DEBUGGING.md References Language Reference: https://ziglang.org/documentation/0.15.2/ Standard Library: https://ziglang.org/documentation/0.15.2/std/ Code Samples: https://ziglang.org/learn/samples/ Zig Guide: https://zig.guide/