Question

I am trying to create alternative names for the function call numberedFunction when it has certain values as below

template< typename T >
class X
{
  public:

    X() : single( std::bind( &X::numberedFunction, *this, 1 ) ),
          halfDozen( std::bind( &X::numberedFunction, *this, 6 ) )
    { ... }

    T numberedFunction( unsigned int i ) { ... }

    const std::function< T() >& single;
    const std::function< T() >& halfDozen;
};

But this code is not correct (segfaults when I try to use any of the specially named functions). Is there an issue with using this the way I am in the initialization list (e.g., is this not guarenteed to be well-formed at the time I am accessing it there)? Something else (obvious)? Is there a better way to do what I am trying to do (I feel like there almost definitely is)?

Answer 1

const std::function< T() >& single;
const std::function< T() >& halfDozen;

Your members are references to const, but you are initializing them from a temporary in the constructor (assuming the bind expressions in your real code aren’t nonsensical). As soon as the construction is done they are invalid. Is this really what you intended?

---

Maybe this is what you want do do (using psychic powers here):

template< typename T >
class X
{
  public:

    X() : single( std::bind( &X::numberedFunction, this, 1 ) ),
          halfDozen( std::bind( &X::numberedFunction, this, 6 ) )
    { ... }

    T numberedFunction( unsigned int i ) { ... }

    const std::function< T() > single;
    const std::function< T() > halfDozen;
};

Notice that I’m binding to this, not *this. This avoids a copy, but may not be what you want.