static_assert'ion that a long and int are the Same Type

Question

So I'm taking a variable from one API, we'll call it long foo and passing it to another API which takes it as the value: int bar.

I'm in visual-studio-2017 in which these are effectively the same thing: https://learn.microsoft.com/en-us/cpp/cpp/data-type-ranges?view=vs-2017

But this will fire:

static_assert(is_same_v<decltype(foo), decltype(bar)>);

Because even though these are effectively the same, they are not the same type. Is there a workaround for this, other than using the numeric limits library to match a long to an int?

The types are not the same. Maybe you want to know if their lengths are the same? — Thomas Matthews, Jan 02 '19 at 20:55
If you ever want to port your code to other platforms, you should *not* assume that `int` and `long` are the same. — Jesper Juhl, Jan 02 '19 at 21:00

score 7 · Accepted Answer · edited Jan 03 '19 at 04:26

long and int are different fundamental types. Even if they are the same size they are not the same type, so is_same_v will never be true. If you want you can check their sizes are the same then proceed with

static_assert(sizeof(foo) == sizeof(bar));

You can even make sure that foo and bar are integral types like

static_assert(sizeof(foo) == sizeof(bar) && 
              std::is_integral_v<decltype(foo)> && 
              std::is_integral_v<decltype(bar)>);

You can also make sure they have the same signedness like

static_assert(sizeof(foo) == sizeof(bar) && 
             std::is_integral_v<decltype(foo)> && 
             std::is_integral_v<decltype(bar)> &&
             std::is_signed_v<decltype(foo)> == std::is_signed_v<decltype(bar)>);

static_assert'ion that a long and int are the Same Type

1 Answers1