If you ever try to define a public custom operator new while keeping the corresponding delete operator private, you’ll end up unable to compile any code that actually invokes the public operator new. The reasoning is quite interesting.

Consider the following code snippet:

#include <cstdlib>

struct Try {
        Try () { /* \o/ */ }

        void *operator new (size_t size) {
            return malloc(size);
        }

    private:
        void operator delete (void *obj) {
            free(obj);
        }
};

int main () {
    Try *t = new Try();

    return 0;
}

An attempt to compile the code leads to this error:

antrikot:~/work/sandbox> g++ try.cc
try.cc: In function ‘int main()’:
try.cc:11: error: ‘static void Try::operator delete(void*)’ is private
try.cc:17: error: within this context
try.cc:11: error: ‘static void Try::operator delete(void*)’ is private
try.cc:17: error: within this context

Although we have never made any (explicit?) use of the private operator delete.
Why does the compiler complain?