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.

Tricks

• Search for pub fn and pub const to quickly skim over the public API of an implementation.
• The same file that contains the implementation of something will often also contain tests for it. Tests can be useful to learn about how to use an API. You can search for test to find them quickly.

Is there any other material on the topic?

• Reading Zig's Standard Library (video)