const std = @import("std");

pub fn Box(comptime T: type) type {
    return struct {
        val: T,
    };
}

pub fn AddBoxType(comptime LHS: type, comptime RHS: type) type {
    const x = std.mem.zeroes(std.meta.FieldType(LHS, .val));
    const y = std.mem.zeroes(std.meta.FieldType(RHS, .val));
    return Box(@TypeOf(x + y));
}

pub fn addbox(lhs: anytype, rhs: anytype) AddBoxType(@TypeOf(lhs), @TypeOf(rhs)) {
    return .{ .val = lhs.val + rhs.val };
}

test {
    std.testing.refAllDecls(@This());
}

test "widen" {
    const foo: Box(u8) = .{ .val = 99 };
    const bar: Box(u16) = .{ .val = 599 };
    const actual = addbox(foo, bar);
    const expected: Box(u16) = .{ .val = 698 };
    try std.testing.expectEqual(expected, actual);
}