Basic Event Emitter in Zig 0.11

EventEmitter.zig

const std = @import("std");
const String = []const u8;
const ListenersList = std.ArrayList(*const fn(String) void);

pub const EventEmitter = struct {
    allocator: *std.mem.Allocator,
    listeners: std.StringHashMap(*ListenersList),

    pub fn init(allocator: *std.mem.Allocator) EventEmitter {
        return EventEmitter{
            .allocator = allocator,
            .listeners = std.StringHashMap(*ListenersList).init(allocator.*)
        };
    }

    pub fn on(self: *EventEmitter, event_type: String, listener: *const fn(String) void) void {
        var maybe_listeners = self.listeners.get(event_type);
        if (maybe_listeners) |listeners| {
            listeners.append(listener) catch unreachable;
        } else {
            var newList = self.allocator.create(ListenersList) catch unreachable;
            newList.* = ListenersList.init(self.allocator.*);
            newList.append(listener) catch unreachable;
            self.listeners.put(event_type, newList) catch unreachable;
        }
    }

    pub fn emit(self: EventEmitter, event_type: String, event_value: String) void {
        var maybe_listeners = self.listeners.get(event_type);
        if (maybe_listeners) |listeners| {
            for (listeners.items) |listener| {
                listener(event_value);
            }
        }
    }
};

main.zig

const std = @import("std");
const Allocator = std.mem.Allocator;
const EventEmitter = @import("./EventEmitter.zig").EventEmitter;
const String = []const u8;

pub fn main() !void {
    var general_purpose_allocator = std.heap.GeneralPurposeAllocator(.{}){};
    var gpa = general_purpose_allocator.allocator();
    var arena = std.heap.ArenaAllocator.init(gpa);
    defer arena.deinit();
    var allocator = arena.allocator();
    
    var event_emitter = EventEmitter.init(&allocator);
    event_emitter.on("yo", &handleEvent);
    event_emitter.emit("yo", "event string value");
}

fn handleEvent(event: String) void {
    const stdout = std.io.getStdOut().writer();
    stdout.print("Received, {s}\n", .{event}) catch unreachable;
}