Question

What is the best pratice in regards to defining a template in C++?

template <class T>
class A
{
private:
    // stuff
public:
    T DoMagic()
    {
        //method body
    }
}

Or:

template <class T>
class A
{
private:
    // stuff
public:
    T DoMagic();
}

template <class T>
A::T DoMagic()
{
    // magic
}

Another way?
I seem to stumble over some controversy regarding this subject.
So; What path to choose?

Answer 1

This is completely a matter of style. That said however:

1. choose a way and stick to it — either all inline, or all out, or mixed based on some rule
2. personally I use a 3 line rule. If the method body in the template is longer than 3 lines I move it outside.

There’s no real reason not to include all definitions inline (they are inline from the compilers POV anyway), however, many people argue that keeping them separate is more clean, and allows the class definition to be more readable.