CODEWITHSUNDEEP
c++templatescontainers
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Reputation: 87361

Restrict C++ template arguments to containers of the same value type

I have a C++ template function:

template<typename Input, typename Output>
void Process(const Input &in, Output *out) {
  ...
}

  1. How can I make it a compile error with a friendly error message if it's called with containers of different types? For example, the call set<int> sout; Process(vector<int>(), &sout); should work, but vector<unsigned> vout; Process(vector<int>(), &vout); should be a compile error.

  2. How can I make it a compile error with a friendly error message if it's called with containers which are not mutually convertible? For example, the calls above should work, but struct A {}; struct B {}; vector<B> vbout; Process(vector<A>(), &vbout); should be a compile error. `

Upvotes: 2

Views: 409

Answers (1)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 153995

You can just static_assert() that the value_types of the two type are the same:

static_assert(std::is_same<typename Input::value_type, typename Output::value_type>::value,
              "the containers passed to Process() need to have the same value_type");

If you want your types to be convertible, you'd use std::is_convertible instead:

static_assert(std::is_convertible<typename Input::value_type, typename Output::value_type>::value,
              "the value_type of the source container passed to Process() needs to be convertible to the value_type of the target container");

Upvotes: 10

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