Badge.h

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/** @noop License Comment
 *  @file
 *  @copyright
 *  This Source Code is subject to the terms of the Mozilla Public License, v2.0.
 *  If a copy of the MPL was not distributed with this file You can obtain one at
 *  https://mozilla.org/MPL/2.0/
 *  
 *  @author David Mórász
 *  @date 2025
 */
 
#pragma once
 
namespace Mcro::Badge
{
    /**
     *  @brief
     *  Use this template to give exclusive access to functions to specific classes.
     *  
     *  Like so:
     *  @code
     *  class A;
     *  class B;
     *  class C;
     *  
     *  class A
     *  {
     *      static void CallFromB(TBadge<B> badge) {...}
     *  };
     *  
     *  class B
     *  {
     *      void Foobar()
     *      {
     *          // OK
     *          A::CallFromB({});
     *      }
     *  };
     *  
     *  class C
     *  {
     *      void Foobar()
     *      {
     *          // compile error:
     *          // badge template instance declared in A::CallFromB is only friends with class B,
     *          // therefore the private default constructor is inaccessible from class C
     *          A::CallFromB({});
     *      }
     *  };
     *  @endcode
     */
    template<class T>
    class TBadge
    {
        friend T;
    private: TBadge() {}
    };
}