CODEWITHSUNDEEP
c++c++11
user1095108
user1095108

Reputation: 14623

recursive std::remove_pointer?

I'm having difficulty with types, such as:

T******************************************

Should std::remove_pointer be able to handle such types at all (I don't think so)? How to remove all the *? If there is an ampersand & or two added at the end, does there exist a metafunction from the C++11 standard to strip such a type down to T without using both the std::remove_reference and std::remove_pointer metafunctions?

Upvotes: 1

Views: 864

Answers (1)

Omnifarious
Omnifarious

Reputation: 56118

It's not too hard to write a meta-function that will return return the base type no matter how many *s and &s you have.

template <typename T>
struct remove_all_ref_ptr { typedef T type; };

template <typename T>
struct remove_all_ref_ptr<T *> : public remove_all_ref_ptr<T> { };

template <typename T>
struct remove_all_ref_ptr<T * const> : public remove_all_ref_ptr<T> { };

template <typename T>
struct remove_all_ref_ptr<T * volatile> : public remove_all_ref_ptr<T> { };

template <typename T>
struct remove_all_ref_ptr<T * const volatile> : public remove_all_ref_ptr<T> { };

template <typename T>
struct remove_all_ref_ptr<T &> : public remove_all_ref_ptr<T> { };

template <typename T>
struct remove_all_ref_ptr<T &&> : public remove_all_ref_ptr<T> { };

And ::std::remove_pointer can handle types like that just fine. It just lops off a single *.

The little meta-function I just wrote will run into the recursion depth limit eventually. But you'll likely have to put on more than a hundred *s to make that happen.

Here is how you might use it in conjunction with a standard library meta-function to remove the const and volatile qualifiers as well:

 #include <type_traits>

 template <typename T>
 struct base_type : public ::std::remove_cv<typename remove_all_ref_ptr<T>::type> { };

Upvotes: 10

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