Sharing a QLatin1String across derived classes: static const vs. inline static const

l3u_

Hi all!

I want to share a QLatin1String across multiple classes derived from the same base class. I found two ways to do this:

Variant 1: I declare it as static const inside BaseClass.h :

class BaseClass
{
    ...
    protected:
        static const QLatin1String someString;
}

and then I declare the value in BaseClass.cpp:

#include "BaseClass.h"
const QLatin1String BaseClass::someString("some string");

Variant 2: I declare the variable as inline static const and assign the value right in BaseClass.h:

class BaseClass
{
    ...
    protected:
        inline static const auto someString = QLatin1String("some string");
}

For both variants, I can access the value via BaseClass::someString in all classes derived from BaseClass.

I'm not sure about this. What is the right way to do it, and why?

Thanks in advance to all the C++ pros for all clarification :-)

Christian Ehrlicher

The only difference is that in variant 2 the optimizer can already optimize away e.g. QLatin1String::size() or other misc functions which need the length of the string.
I doubt it makes any difference in speed here.

l3u_

So this is more a question of programming style? Does it have any other implication? Besides the fact that I cheap out the line of code needed in variant 1 in the cpp file? Or is variant 1 still around because variant 2 was not possible before C++17?

Christian Ehrlicher

@l3u_ said in Sharing a QLatin1String across derived classes: static const vs. inline static const:

Or is variant 1 still around because variant 2 was not possible before C++17?

correct

l3u_

Well okay, then I'll go for variant 2 – seems more logical to me to declare such a shared const variable right away instead of having to re-reference it inside the implementation.

Thanks for the clarification :-)