@[Extern]
struct Foo
  @x = 0_i64
  @y = 0_i128
end

foo = Foo.new
pointerof(foo.@x) # => Pointer(Int128)@0x7fffd4e08e60
pointerof(foo.@y) # => Pointer(Int128)@0x7fffd4e08e68
offsetof(Foo, @y) # => 8
sizeof(Foo)       # => 24
alignof(Foo)      # => 8

pointerof(foo.@x) # => Pointer(Int64)@0x16f6d3340
pointerof(foo.@y) # => Pointer(Int128)@0x16f6d3350
offsetof(Foo, @y) # => 16
sizeof(Foo)       # => 32
alignof(Foo)      # => 16