eql

pub fn eql(a: anytype, b: @TypeOf(a)) bool {
    const T = @TypeOf(a);

    switch (@typeInfo(T)) {
        .@"struct" => |info| {
            if (info.layout == .@"packed") return a == b;

            inline for (info.field_names) |field_name| {
                if (!eql(@field(a, field_name), @field(b, field_name))) return false;
            }
            return true;
        },
        .error_union => {
            if (a) |a_p| {
                if (b) |b_p| return eql(a_p, b_p) else |_| return false;
            } else |a_e| {
                if (b) |_| return false else |b_e| return a_e == b_e;
            }
        },
        .@"union" => |info| {
            if (info.layout == .@"packed") return a == b;
            const UnionTag = info.tag_type orelse
                @compileError("cannot compare untagged union type " ++ @typeName(T));

            const tag_a: UnionTag = a;
            const tag_b: UnionTag = b;
            if (tag_a != tag_b) return false;

            return switch (a) {
                inline else => |val, tag| return eql(val, @field(b, @tagName(tag))),
            };
        },
        .array => {
            for (a, b) |x, y| {
                if (!eql(x, y)) return false;
            }
            return true;
        },
        .vector => return @reduce(.And, a == b),
        .pointer => |info| {
            return switch (info.size) {
                .one, .many, .c => a == b,
                .slice => a.ptr == b.ptr and a.len == b.len,
            };
        },
        .optional => {
            const some_a = a orelse return b == null;
            const some_b = b orelse return false;
            return eql(some_a, some_b);
        },
        else => return a == b,
    }
}