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// file : butl/const-ptr -*- C++ -*-
// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
// license : MIT; see accompanying LICENSE file
#ifndef BUTL_CONST_PTR
#define BUTL_CONST_PTR
#include <cstddef> // nullptr_t
namespace butl
{
// Const-propagating pointer.
//
// It has the semantics of a raw pointer except that it passes on its own
// const-ness to the pointed-to object. In other words, if you have a const
// instance of this pointer, then you can only obtain a const raw pointer to
// the underlying object. It is normally used as a data member, for example:
//
// struct tree
// {
// const_ptr<tree> left;
// const_ptr<tree> right;
//
// void modify ();
// };
//
// tree* x = ...;
// const tree* y = ...;
//
// x.left->modify (); // Ok.
// y.left->modify (); // Error.
//
// Note that due to this semantics, copy construction/assignment requires
// a non-const instance of const_ptr.
//
// Known drawbacks/issues:
//
// 1. Cannot do static_cast<mytree*> (x.left).
//
template <typename T>
class const_ptr
{
public:
const_ptr () = default;
explicit const_ptr (T* p): p_ (p) {}
const_ptr (std::nullptr_t): p_ (nullptr) {}
const_ptr& operator= (T* p) {p_ = p; return *this;}
const_ptr& operator= (std::nullptr_t) {p_ = nullptr; return *this;}
template <class T1> explicit const_ptr (T1* p): p_ (p) {}
template <class T1> const_ptr (const_ptr<T1>& p): p_ (p.p_) {}
template <class T1> const_ptr& operator= (T1* p) {p_ = p; return *this;}
template <class T1> const_ptr& operator= (const_ptr<T1>& p) {
p_ = p.p_; return *this;}
T* operator-> () {return p_;}
const T* operator-> () const {return p_;}
T& operator* () {return *p_;}
const T& operator* () const {return *p_;}
operator T* () {return p_;}
operator const T* () const {return p_;}
explicit operator bool () const {return p_ != nullptr;}
T* get () {return p_;}
const T* get () const {return p_;}
private:
T* p_;
};
};
#endif // BUTL_CONST_PTR
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