CODEWITHSUNDEEP
c++c++11variadic-functions
Channel72
Channel72

Reputation: 24739

Variadic templates: Pass parameter pack without expansion

The old C stdio facilities provided a way to pass along a variadic argument set using the vprintf facilities.

Is there a similar way to pass along a C++0x variadic template parameter pack without expanding it?

This might be useful if you have a derived class constructor that takes a variadic template parameter pack, and needs to simply pass it on to the base class constructor, rather than unpacking it.

For example:

template <class T, class... Args>
Base::Base(const T& v, const Args&... args) 
{
  /*...expand args here ....*/
}

template <class T, class... Args>
Derived::Derived(const T& v, const Args&... args) : Base(v, args)
{
  /*...don't expand args...*/
}

I thought you could simply pass around the args parameter pack without expanding it, by excluding the ... after the args, but this simply results in a compiler error on GCC 4.3:

 error: parameter packs not expanded with `...'

So it is possible to pass along the parameter pack without expanding it?

Upvotes: 4

Views: 4627

Answers (1)

icecrime
icecrime

Reputation: 76835

I don't understand how expanding is an issue : won't expanded arguments be just re-packed in Base constructor ? I believe using args... will work as expected.

Upvotes: 7

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