How to read the standard library source code

Where is the stdlib code located?

You can find it under /lib/std/.

How is the stdlib structured?

When you import "std" in a Zig source file, you are importing /lib/std/std.zig.

const std = @import("std");

In that file you can see where each exposed symbol comes from:

// Excerpt from std.zig
...
pub const ArrayHashMap = array_hash_map.ArrayHashMap;
pub const ArrayHashMapUnmanaged = array_hash_map.ArrayHashMapUnmanaged;
pub const ArrayList = @import("array_list.zig").ArrayList;
pub const ArrayListAligned = @import("array_list.zig").ArrayListAligned;
pub const ArrayListAlignedUnmanaged = @import("array_list.zig").ArrayListAlignedUnmanaged;
pub const ArrayListUnmanaged = @import("array_list.zig").ArrayListUnmanaged;
...

Some parts of the stdlib are simple and are implemented in a single file, like std.ascii, which is entirely implemented in /lib/std/ascii.zig.

Other parts of the standard library are beefier and have their own dedicated subdirectory, like std.math. These "submodules" always have a regular structure:

• A subdirectory that contains most of the implementation
• A file inside /lib/std/ that exposes the public parts implemented in the relative subdirectory

In the case of std.math, for example, /lib/std/math/ceil.zig contains the implementation of ceil that /lib/std/math.zig then re-exports like this:

pub const ceil = @import("math/ceil.zig").ceil; 

The directory tree of the std.ascii and std.math files described above looks like this:

.
`-- lib/
    `-- std/
        |-- ascii.zig
        |-- math/
        |   `-- ceil.zig
        `-- math.zig

With this knowledge it should be easy for you to track down the implementation code of every symbol defined in the standard library.

One final trick: search for pub fn and pub const to quickly skim over the public API of an implementation.

Is there any other material on the topic?

• Reading Zig's Standard Library (video)