BOOST_STATIC_ASSERT without boost

Question

Since boost is forbidden in a company I work for I need to implement its functionality in pure C++. I\'ve looked into boost sources but they seem to be too complex to unders

Answer 1

Here is my own implementation of static assertions extracted from my code base: Pre-C++11 Static Assertions Without Boost.

Usage:

STATIC_ASSERT(expression, message);

When the static assertion test fails, a compiler error message that somehow contains the STATIC_ASSERTION_FAILED_AT_LINE_xxx_message is generated.

message has to be a valid C++ identifier, like no_you_cant_have_a_pony which will produce a compiler error containing:

STATIC_ASSERTION_FAILED_AT_LINE_1337_no_you_cant_have_a_pony :)

#define CONCATENATE(arg1, arg2)   CONCATENATE1(arg1, arg2)
#define CONCATENATE1(arg1, arg2)  CONCATENATE2(arg1, arg2)
#define CONCATENATE2(arg1, arg2)  arg1##arg2

/**
 * Usage:
 *
 * STATIC_ASSERT(expression, message)
 *
 * When the static assertion test fails, a compiler error message that somehow
 * contains the "STATIC_ASSERTION_FAILED_AT_LINE_xxx_message" is generated.
 *
 * /!\ message has to be a valid C++ identifier, that is to say it must not
 * contain space characters, cannot start with a digit, etc.
 *
 * STATIC_ASSERT(true, this_message_will_never_be_displayed);
 */

#define STATIC_ASSERT(expression, message)\
  struct CONCATENATE(__static_assertion_at_line_, __LINE__)\
  {\
    implementation::StaticAssertion((expression))> CONCATENATE(CONCATENATE(CONCATENATE(STATIC_ASSERTION_FAILED_AT_LINE_, __LINE__), _), message);\
  };\
  typedef implementation::StaticAssertionTest CONCATENATE(__static_assertion_test_at_line_, __LINE__)

  // note that we wrap the non existing type inside a struct to avoid warning
  // messages about unused variables when static assertions are used at function
  // scope
  // the use of sizeof makes sure the assertion error is not ignored by SFINAE

namespace implementation {

  template 
  struct StaticAssertion;

  template <>
  struct StaticAssertion
  {
  }; // StaticAssertion

  template
  struct StaticAssertionTest
  {
  }; // StaticAssertionTest

} // namespace implementation


STATIC_ASSERT(true, ok);
STATIC_ASSERT(false, ko);

int main()
{
  return 0;
}