Can I typedef a template template parameter?

Question

In C++ library headers, we'll sometimes see the following to improve legibility of the code inside a class:

template<typename MyExplicitelyLongTemplateParameter>
class C
{
public:
    typedef MyExplicitelyLongTemplateParameter P;

    // Use "P" and keep your sanity.
};

My question is, can one do the same with template template parameter?

template<template<typename> typename MyExplicitelyLongTemplateParameter>
class C
{
public:
    typedef /* ??? */ P;

    // Use "P" and keep your sanity.
};

I haven't come across this syntax before. What does it do? – yuriks May 01 '11 at 03:34 — yuriks, May 01 '11 at 03:34
I think that should be template – ymett May 01 '11 at 07:30 — ymett, May 01 '11 at 07:30

score 8 · Answer 1 · answered May 01 '11 at 02:22

8

You can't create a typedef, no, but you can shorten the name:

template <template <typename> typename MyExplicitlyLongTemplateParameter>
class C
{
public:

    template <typename T>
    struct P 
    {
        typedef MyExplicitlyLongTemplateParameter<T> Type;
    };

    // Use "P<T>::Type" and keep your sanity.
};

answered May 01 '11 at 02:22

James McNellis

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+1, but as noted in the comments above, it should really be ` – Vitus May 01 '11 at 10:27

score 3 · Answer 2 · answered May 01 '11 at 02:19

3

In the current standard, you can't typedef a template. In the new, upcoming standard, you will be able to....

answered May 01 '11 at 02:19

jwismar

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And how will someone be able to typedef in the new standard? – Werner Feb 26 '15 at 20:50

Can I typedef a template template parameter?

2 Answers2

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