Re: Heterogeneous collection: return type overload

Victor Bazarov <>
Wed, 17 Feb 2010 13:48:48 -0500
jrbcast wrote:

Imagine I have something like this:

class Collection
    std::map<char *, void *> elements;

    addElement( char * name, void * value )

/*** I Want to merge next methods into a single one ***/
    int getValue( char * name )

    double getValue( )


The purpose of this code would be to have a collection of objects of
different kind. Supposing that inside the class I would be able to
know which is the type of each element... How could I implement a
single function to return the right type?

What's the "right type"? How do you know which type is right? In most
systems I've seen folks didn't use the return value. They used an
argument or a template argument.


     bool getValue(char const* name, int& ri)
        // assign to 'ri' if found, return true
        // if not found, don't touch 'ri' return false

     bool getValue(char const* name, double& rd) // same thing

Template argument:

     template<class T> T getValue(char const* name)
        return SomeHelperClassYouCanSpecialize<T>(this, name);

Both solutions require the caller to know which type is right.
Otherwise you need a dynamically typed system, and it ain't C++.

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