Item 11: Prefer Deleted Functions to Private Undefined Ones

Delete functions replace the private-undefined-function trick and there are some nice tricks that only delete functions can do.

Deleted functions should be declared public because compiler checks accessibility before deleted status.

(vs private-undefined-function trick) Deleted functions err during compile time, not until link time.

Trick 1: Disable certain implicit parameter type conversion:

bool isLucky(int number);
bool isLucky(char) = delete;
bool isLucky(bool) = delete;
bool isLucky(double) = delete;
// Why no isLucky(float)?
// When present a float,
// C++ prefers convertint it
// to a double than int.

Trick 2: Disable certain template instantiations:

template<typename T>
void foo(T* ptr);

template<>
void foo<void>(void*) = delete;

template<>
void foo<const void>(const void*) = delete;