ArrayList in Zig

The growable list is unmanaged: every append hands the allocator in explicitly.

const std = @import("std");

pub fn main() !void {
    var gpa = std.heap.DebugAllocator(.{}){};
    defer _ = gpa.deinit();
    const alloc = gpa.allocator();

    // ArrayList is unmanaged: every growing call takes the allocator.
    var hauls = std.ArrayList(f32).empty;
    defer hauls.deinit(alloc);

    try hauls.append(alloc, 12.5);
    try hauls.append(alloc, 8.0);
    try hauls.appendSlice(alloc, &.{ 15.25, 6.75 });

    std.debug.print("{d} hauls logged\n", .{hauls.items.len});
    const last = hauls.items[hauls.items.len - 1];
    std.debug.print("first {d:.2}, last {d:.2}\n", .{ hauls.items[0], last });
}

How it works

1. std.ArrayList(f32).empty starts with no storage at all.
2. append and appendSlice take alloc because growing might allocate.
3. .items is the live slice: index it, measure it, read it back.

Keywords and builtins used here

• const
• defer
• f32
• fn
• pub
• try
• var
• void

The run, in numbers

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19

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Type this snippet

Step 2 of 3 in Memory, step 20 of 27 in Language basics.

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