zig-arraylist

name	zig-arraylist
description	Reference for Zig 0.15+ ArrayList API which passes the allocator to each method call instead of at initialization. Use when working with ArrayLists in Zig 0.15+.

Zig 0.15 ArrayList API

This project uses Zig 0.15 which has a different ArrayList API than earlier versions.

Key Differences from Older Zig Versions

Initialization

Old (pre-0.15):

var list = std.ArrayList(T).init(allocator);

New (0.15+):

var list = std.ArrayList(T){};

The allocator is NOT passed at initialization. Instead, it's passed to each method call.

Common Operations

Append:

// Old
try list.append(item);

// New (0.15)
try list.append(allocator, item);

Deinit:

// Old
list.deinit();

// New (0.15)
list.deinit(allocator);

AppendSlice:

// Old
try list.appendSlice(items);

// New (0.15)
try list.appendSlice(allocator, items);

ToOwnedSlice:

// Old
const slice = try list.toOwnedSlice();

// New (0.15)
const slice = try list.toOwnedSlice(allocator);

Complete Example

const std = @import("std");

fn example(allocator: std.mem.Allocator) ![]u32 {
    // Initialize without allocator
    var list = std.ArrayList(u32){};
    defer list.deinit(allocator);

    // All operations take allocator as first arg
    try list.append(allocator, 1);
    try list.append(allocator, 2);
    try list.append(allocator, 3);

    // Convert to owned slice
    return try list.toOwnedSlice(allocator);
}

Why This Change?

Zig 0.15 moved to a more explicit allocator passing style. This makes it clearer where allocations happen and allows using different allocators for different operations on the same list.

Common Error Messages

If you see errors like:

• struct 'array_list.Aligned(T,null)' has no member named 'init'
• expected 2 argument(s), found 1

You're likely using the old API. Update to the new pattern shown above.