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

您不能重载运算符newto be constexpr，主要问题归因于 C++ 标准指令\xc2\xa79.1.5/1constexpr说明符 [dcl.constexpr]（强调我的）：

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说明constexpr符仅应用于变量或变量模板的定义或者函数或函数模板的声明。使用\n 说明符声明的函数或静态数据成员 constexpr隐式是内联函数或变量\n (9.1.6)。如果函数或函数模板的任何声明具有\n constexpr说明符，则其所有声明都应包含\n constexpr说明符。

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也就是说，为了重载运算符，new其之前的所有声明也必须是constexpr，但它们不是，因此在constexpr出现编译时错误时会重载它。

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