Constexpr operator new

Question

Is it possible to overload the operator new to be constexpr function? Something like:

constexpr void * operator new( std::size_t count );

The reason why would be to execute constexpr function within the overloaded operator body where count argument value would be an input data... As the operator is invoked by:

SomeClass * foo = new SomeClass(); 

The size of the data type is know at compile time, isn’t it? (count== sizeof(SomeClass)) So the count can be considered as compile time constant?

constexpr void * operator new( std::size_t count )
{
  if constexpr ( count >= 10 ) { /* do some compile-time business */ }
}

Many thanks in advance to anyone willing to help!

Answer 1

You can't overload operator new to be constexpr, the main problem is attributed to the C++ standard directive §9.1.5/1 The constexpr specifier [dcl.constexpr] (Emphasis Mine):

The constexpr specifier shall be applied only to the definition of a variable or variable template or the declaration of a function or function template. A function or static data member declared with the constexpr specifier is implicitly an inline function or variable (9.1.6). If any declaration of a function or function template has a constexpr specifier, then all its declarations shall contain the constexpr specifier.

That is, in order to overload operator new all its previous declarations must also be constexpr, which they aren't and thus overloading it as constexpr you get a compile time error.