CODEWITHSUNDEEP
c++c++11
Greencpp
Greencpp

Reputation: 155

Can a "type" be passed in C++?

[A follow up to this question: Possible to instantiate object given its type in C++?

In Java, you can have a method parameter of type Class, and callers can pass in Foo.class. I don't consider this aspect reflection, though what you can do with the passed-in Class obviously is. Does C++ have any mechanism for passing in a "type"? Since I know there is little/nothing I could do with that passed-in type, I suspect the answer is "no".

Obviously, templates provide this facility, but they're not what I'm looking for.

Upvotes: 3

Views: 328

Answers (3)

Billy ONeal
Billy ONeal

Reputation: 106539

No. This feature is part of "reflection" and is only possible in languages like Java which actually put information about classes in the compiled binary.

C++ (typically) does not actually store any information about classes at all in the resulting binary. (Excepting a few bits necessary for std::type_info to work)

In reality, there's nothing like the "Type" provided by Java and friends available in C++, and therefore you cannot pass it to a method.

If you want to pass a type to a method for the purpose of instantiating it, you can actually do this in a better way (this works with Java and friends too)

#include <memory>

struct IMyType
{
    virtual ~IMyType();
    virtual MyMethod();
};

struct IElementFactory
{
    virtual std::auto_ptr<IMyType> GetNewItem() const = 0;
    virtual ~IElementFactory();
};


void MyMethodThatAcceptsAType(const IElementFactory& factory)
{
    std::auto_ptr<IMyType> instance(factory.GetNewItem());
    //Use your instance like normal.
}

This is better even in Java land because this code maintains type safety, while the reflection based code does not.

Upvotes: 0

Bert F
Bert F

Reputation: 87533

How about RTTI and typeid?

Upvotes: 0

Laurence Gonsalves
Laurence Gonsalves

Reputation: 143154

Sounds like RTTI (run-time type identification) is what you're looking for. From http://en.wikibooks.org/wiki/C++_Programming/RTTI :

The typeid operator, used to determine the class of an object at runtime. It returns a reference to a std::type_info object, which exists until the end of the program, that describes the "object".

Upvotes: 4

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