CODEWITHSUNDEEP
c++classtemplatestemplate-specialization
Marcin Poloczek
Marcin Poloczek

Reputation: 993

How to force template class to use specified type unless specified otherwise?

I have problem with my template class. I specified default type of my template class like that:

template < class T = float >
class apple { 
public:
    T x;
    apple(T x): x(x) {}
}

However, when I create the object like that:

apple obj(2);

The type turns into int unless I do that:

apple<float> obj(2);

How would I make it stay float?

Upvotes: 4

Views: 213

Answers (3)

HolyBlackCat
HolyBlackCat

Reputation: 96071

Another possible solution is to modify the constructor:

apple(std::enable_if_t<1, T> x): x(x) {}

This way the compiler won't be able to deduce T from an argument you pass to x, and will use the default type for T (that you provided) instead.

Upvotes: 1

Quentin
Quentin

Reputation: 63124

Add this deduction guide to force all argument deductions to resolve to your default arguments:

template <class T>
apple(T) -> apple<>;

Upvotes: 5

Vlad from Moscow
Vlad from Moscow

Reputation: 310950

Use the specialization for the default template parameter like

apple<> obj( 2 );

Upvotes: 3

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