Why there is no placement delete expression in C++?

Solution 1:

operator delete is unique in being a non-member or static member function that is dynamically dispatched. A type with a virtual destructor performs the call to its own delete from the most derived destructor.

struct abc {
    virtual ~abc() = 0;
};

struct d : abc {
    operator delete() { std::cout << "goodbye\n"; }
};

int main() {
    abc *p = new d;
    delete p;
}

(Run this example.)

For this to work with placement delete, the destructor would have to somehow pass the additional arguments to operator delete.

• Solution 1: Pass the arguments through the virtual function. This requires a separate virtual destructor for every static member and global operator delete overload with different arguments.
• Solution 2: Let the virtual destructor return a function pointer to the caller specifying what operator delete should be called. But if the destructor does lookup, this hits the same problem of requiring multiple virtual function definitions as #1. Some kind of abstract overload set would have to be created, which the caller would resolve.

You have a perfectly good point, and it would be a nice addition to the language. Retrofitting it into the existing semantics of delete is probably even possible, in theory. But most of the time we don't use the full functionality of delete and it suffices to use a pseudo-destructor call followed by something like arena.release(p).

Solution 2:

Probably because there was syntax for explicitly calling a destructor without deallocation (exactly as in your question), but no syntax for explicit construction in raw memory?

Solution 3:

Actually there is a placement delete which is called by the implementation for an object that was "allocated" using placement new if the constructor threw an exception.

From Wikipedia.

The placement delete functions are called from placement new expressions. In particular, they are called if the constructor of the object throws an exception. In such a circumstance, in order to ensure that the program does not incur a memory leak, the placement delete functions are called.