Zig minimal generic callback example (slimmed version of TigerBeetle IO struct)

callback_example.zig

pub const Transport = struct {
    pub fn send(
        self: *Transport,
        comptime Context: type,
        context: Context,
        comptime callback: fn (
            context: Context,
            reuslt: usize,
        ) void,
    ) void {
        callback(context, 1);
    }
};

const std = @import("std");
const testing = std.testing;

test "Transport" {
    const Context = struct {
        t: Transport,
        result: usize = undefined,

        const Self = @This();

        fn onSend(self: *Self, result: usize) void {
            self.result = result;
        }

        fn run(self: *Self) void {
            self.t.send(*Self, self, onSend);
        }
    };

    var ctx = Context{ .t = Transport{} };
    ctx.run();
    try testing.expectEqual(@as(usize, 1), ctx.result);
}

$ zig test callback_example.zig 
All 1 tests passed.
$ zig version
0.8.1

The above example is based on TigerBeetle IO.send method