CODEWITHSUNDEEP
c++constantsstatic-methods
Pietro
Pietro

Reputation: 13160

Const static member functions: is another approach available?

As reported in this Q&A, const static member functions are/were not available in C++. Did anything change since then (2011)?

Is there another way to have static member functions that do not modify the static members of their class?

Something like (pseudo-code):

class C
{
   static int a;
public:
   static void Incr() { ++a; }
   static int  Ret() const { return a; }
};

int C::a = 0;

I would need to call a [const] static member function from another class' const member function.

Upvotes: 2

Views: 139

Answers (3)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170065

Did anything change since then (2011)?

Nothing changed, you still can't cv-qualify a static member function.

Is there another way to have static member functions that do not modify the static members of their class?

Not a perfect solution, but you may declare const "aliases" to static data members:

static int  Ret() { 
    static constexpr const auto& a = C::a;
    // Now C::a is shadowed by the local a
    // and the function can't modify it.
    // a = 2; // ill-formed
    return a * 2; // OK
}

It still requires discipline, but at least that way a compiler can catch unintended modification attempts.

Upvotes: 5

Marek R
Marek R

Reputation: 37647

Class which has only static fields and static methods doesn't deserve to be called class. It is just form of functions and global variables with fancy name spacing.

Anyway IMO it is much better to have a regular class with regular fields and methods and then instantiate it as a global variable (not very nice solution, but at least more honest where class contains only static fields and methods).

class C
{
   int a;
public:
   C() : a(0) {}
   void Incr() { ++a; }
   int  Ret() const { return a; }
};

C instance;

Or use singleton pattern which I hate.

From generated code perspective there should be no difference.

Upvotes: 3

eike
eike

Reputation: 1334

According to the current cppreference.com (page about static members), static member functions still cannot be const, because the const keyword only modifies the this pointer, which static functions obviously do not have.

So nothing seems to have changed since the answer you were referring to was written.

Upvotes: 8

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