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Procedural code gets information then makes decisions. Object-oriented code tells objects to do things.

Alec Sharp

When we are using the Factory pattern, we make decision, based on a property of a class except than the factory class, so this, doesn't violate Tell, Don't Ask principle?

Gordon
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Masoud
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1 Answers1

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No, we don't violate.

When we tell the Factory class to create an object instance, all the responsibility is within the Factory class. The caller has no influence what the concrete class will be.

The Factory class itself also doesn't break that rule. It is doing what it has to do: based on the given rules (let it be hard-coded or externally set, or maybe something more complex) decides what kind of object to generate. But every bit of the logic is inside the factory method.

gaborsch
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  • but e.g, the Factory class is making decision, based on Product state in http://www.oodesign.com/factory-pattern.html example. (asking product, and then making decision) – Masoud Jul 26 '13 at 08:01
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    You mean based on the product ID? that's not a problem, because only the Factory class can know about all possible classes and it has the logic to decide which one to use. You cannot delegate this responsibility to any other class. – gaborsch Jul 26 '13 at 08:08