What other useful casts can be used in C++

Question

C++ comes with four built-in casts.

1. static_cast
2. dynamic_cast
3. const_cast
4. reinterpret_cast

Not to meantion the frowned upon C (style*)cast.

Additionally boost supplies a lexical_cast, are there any other useful casts that you use or would like to exist?

Answer 1

My favorite and most loved cast is implicit_cast. It only succeeds if the types can be implicitly converted.

Useful for conversion from some type into void* or from some derived class into a base (if you want to select a specific instance of an overloaded function or constructor) or to safely add const-qualifications and any other scenario where you really just need implicit conversions to happen and even static_cast is too powerful.

Also read How does C++ pick which overload to call.

boost/implicit_cast.hpp. You can add this to your code collection too, if you want

template<typename T> struct identity { typedef T type; };
template<typename Dst> Dst implicit_cast(typename identity<Dst>::type t)
{ return t; }

Answer 2

There's also the function-style cast which looks like a function or constructor call. This resolves to the constructor call for classes, and (more generally) to C-style casts for all other types.

Examples:

int x = int(1.0);       // equals `(int)1.0`
string s = string("x"); // equals call to constructor

The call to a constructor can also be achived using an explicit cast (apart from the C-style cast which would also work):

string s = static_cast<string>("x"); // is the same as above!