CODEWITHSUNDEEP
c++c++11partial-specialization
abir
abir

Reputation: 1797

can template alias be used for partial specialization?

Given a template alias

template<unsigned U>
using uint_ = integral_constant<unsigned,U>;

The partial specialization of

template<class T,class P>
struct size{};

as

template <class T,unsigned U>
struct size<T,uint_<U>>{};

generates a warning astemplate parameter can not be deduced for clang 3.1 while no warning is generated with gcc 4.7

So, is it malformed code?

Upvotes: 4

Views: 824

Answers (2)

Johannes Schaub - litb
Johannes Schaub - litb

Reputation: 506897

Another guy said that this is a Clang bug. You can work it around if you change the using declaration like this

template<unsigned T, unsigned U = T>
using uint_ = integral_constant<unsigned,U>;

As an educated guess, apparently Clang does not correctly update the identity of the template parameter that appears in the type-id. So it thinks in your example that the resulting type uint_<U> refers to the first parameter of the partial specialization (because within uint_ that is the case, but not in the point of use). Alternatively you can exchange the order at the point of use

template <unsigned U,class T>
struct size<T,uint_<U>>{};

Upvotes: 3

Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361322

The code is perfectly fine in C++11. The Clang's warning can be ignored.

Upvotes: 5

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