CODEWITHSUNDEEP
c++gccc++11static-assert
GuiTeK
GuiTeK

Reputation: 1731

static_assert that checks if template parameter type is accepted by another function

I have a function template defined as follows:

template <typename T>
Test &operator<<(const T &data)
{
    std::cout << data << std::endl;
    return *this;
}

As you can see, I print out to the console data using std::cout, which type is std::ostream. However, T may not be a type handled by std::ostream::operator<<.

That's why I'd like to add a static_assert to check whether T is accepted by the insertion operator or not. Currently, I must do a check for every type that std::ostream::operator<< accept:

template <typename T>
Test &operator<<(const T &data)
{
    static_assert(std::is_arithmetic<T>::value ||
                  std::is_same<T, std::streambuf*>::value ||
                  ...
                  std::is_same<T, std::string>::value, "data type must be compliant to std::ostream::operator<< accepted types");

    std::cout << data << std::endl;
    return *this;
}

Is there a type trait that automatically do that? What would you do?

Upvotes: 0

Views: 1392

Answers (1)

Jonathan Wakely
Jonathan Wakely

Reputation: 171263

Why do you want a static_assert? Is it acceptable to simply make the function not callable if the insertion isn't valid?

template <typename T>
auto operator<<(const T &data) -> decltype(std::cout << data, std::declval<Test&>())
{
    std::cout << data << std::endl;
    ...
}

If you really want a trait see is_stream_insertable

Upvotes: 2

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