Trick to print `sizeof(type)` as a compiler error

sizeof_as_compiler_error.h

#pragma once

#define sizeof_as_compiler_error(type) struct sizeof__##type##__is* (*sizeof__##type)[sizeof(type)] = -1;

usage_examples.cpp

// Try it online https://godbolt.org/z/hfsxEE

#define sizeof_as_compiler_error(type) struct sizeof__##type##__is* (*sizeof__##type)[sizeof(type)] = -1;

struct EmptyStruct
{
};

enum class tribool : signed char
{
    Undefined = -1,
    False = 0,
    True = 1,
};

sizeof_as_compiler_error(bool)         // sizeof == 1, printed in error: cannot initialize a variable of type 'struct sizeof__bool__is *(*)[1]' with an rvalue of type 'int'
sizeof_as_compiler_error(tribool)      // sizeof == 1, printed in error: cannot initialize a variable of type 'struct sizeof__tribool__is *(*)[1]' with an rvalue of type 'int'
sizeof_as_compiler_error(int)          // sizeof == 4, printed in error: cannot initialize a variable of type 'struct sizeof__int__is *(*)[4]' with an rvalue of type 'int'
sizeof_as_compiler_error(EmptyStruct)  // sizeof == 1, printed in error: cannot initialize a variable of type 'struct sizeof__EmptyStruct__is *(*)[1]' with an rvalue of type 'int'