CODEWITHSUNDEEP
c++c++11templates
Sudeep Agarwal
Sudeep Agarwal

Reputation: 37

Compile time if else in c++ 11

I have this template function -

template <int N> 
void foo() {
  if (N < 2) {
    bar1();
  } else {
    bar2();
  }
}

I want to deduce if else during compile time in C++11 to make the function efficient. I thought of adding an additional template bool variable like this -

template <int N, bool I = (N < 2), std::enable_if<I>> 
void foo() {
    bar1();
}
template <int N, bool I = (N < 2), std::enable_if<!I>> 
void foo() {
    bar2();
}

Not sure if this is the right approach. Can anyone please help?

Upvotes: 0

Views: 1032

Answers (1)

cigien
cigien

Reputation: 60208

In C++11, you can use enable_if to write 2 overloads

template <int N, typename std::enable_if<N < 2, int*>::type = nullptr> 
void foo() {
    bar1();
}

template <int N, typename std::enable_if<N >= 2, int*>::type = nullptr> 
void foo() {
    bar2();
}

Here's a demo

Note that this is unlikely to give you any performance advantage. Compilers will be able to use the template parameter N in the if condition to remove the unneeded branch.

Upvotes: 2

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