CODEWITHSUNDEEP
c++this
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Reputation: 12652

Passing this by value

Silly question: what is the best way to pass this by value?

Background: Let's use cars and car options. I used to have constructors such as Ford(FordOptions), Honda(HondaOptions). All cars derive from Car, all options from CarOptions. I used to have a car factory that gets passed a pointer to a CarOption, checks the type, produces the appropriate car, and returns a pointer to a generic Car.

I have now changed this so that CarOption has a virtual ProduceCar returning a Car, and every individual car option implements its particular production. So when I get a generic pointer to a car option, I just call CarOptions.ProduceCar and get a generic pointer to a car.

This is all fine, except in the implementation for say FordOption.ProduceCar I need to pass the FordOption instance to the Ford constructor. I can do this by passing "this" and changing the constructur for Ford to accept a pointer to FordOptions instead of FordOptions. However, I'd like it to take FordOptions by value, or at least by reference, but struggle to do so.

Long question for a simple answer I bet. Thanks.

Upvotes: 2

Views: 176

Answers (5)

ventaur
ventaur

Reputation: 1851

I believe you want to dereference the 'this' pointer. To do so, send *this to your contsructor.

Upvotes: 1

Ferdinand Beyer
Ferdinand Beyer

Reputation: 67147

If all you want to do is to path this by value or reference, just use *this:

return new Ford(*this);

Upvotes: 1

Dennis Zickefoose
Dennis Zickefoose

Reputation: 10969

this is a regular old pointer. So *this produces a reference to the object this points to, which can then be passed however you like.

Upvotes: 1

crazyscot
crazyscot

Reputation: 11989

So you have a CarOption& which you believe is in fact a FordOption& ? Sounds like a job for the dynamic_cast operator.

Upvotes: 0

king_nak
king_nak

Reputation: 11513

You just have to dereference the this pointer... And depending on the called method, you pass a reference (as in the example), or by value

Ford::Ford(const FordOption &o) {}

Ford FordOption::produceCar() {
   return Ford(*this); // <-- Dereference this
}

Upvotes: 4

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