Search ArrayList of Structs in zig

Question

I expect this is a question with a very simple answer about how to do this well in zig.

I want to search an ArrayList of some struct to find a record by one of the fields.
In C++ I would consider using std::find_if and a lambda but there doesn't seem to be anything like this in the zig standard library unless I missed something.

Is there a better / more idiomatic way than the simple loop like below?

const std = @import("std");

const Person = struct {
    id: i32,
    name: []const u8
};

pub fn main() !void {

    const allocator = std.heap.page_allocator;

    var data = std.ArrayList(Person).init(allocator);
    defer data.deinit();

    try data.append(.{.id = 1, .name = "John"});
    try data.append(.{.id = 2, .name = "Dave"});
    try data.append(.{.id = 8, .name = "Bob"});
    try data.append(.{.id = 5, .name = "Steve"});

    // Find the id of the person with name "Bob"
    //
    // -- IS THERE A BETTER WAY IN ZIG THAN THIS LOOP BELOW? --
    //
    var item_index: ?usize = null;
    for (data.items) | person, index | {
        if (std.mem.eql(u8, person.name, "Bob")) {
            item_index = index;
        }
    }

    std.debug.print("Found index is {}\n", .{item_index});


}

Kitsu · Accepted Answer · 2021-06-11 17:50:14Z

5

There's not that many built-in utilities present in stdlib, indeed. However, for that piece of code, you may declare the found index as a const:

const item_index = for (data.items) |person, index| {
    if (std.mem.eql(u8, person.name, "Bob")) break index;
} else null;

answered Jun 11, 2021 at 17:50

Kitsu

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