CODEWITHSUNDEEP
c#oop
user20358
user20358

Reputation: 14736

OOPs whats happening here in this assignment

I came across these lines of code

ClassA classAObject;
//some lines of code that hydrate 'classAObject'
DerivedFromClassA derivedObject = classAObject as DerivedFromClassA;

whats going on, on the last line? Is it assigning to derivedObject only those values that are in common between derivedObject and classAObject ?

Upvotes: 3

Views: 192

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1500923

No, it's broadly equivalent to:

DerivedFromClassA derivedObject = null;
if (classAObject is DerivedFromClassA)
{
    derivedObject = (DerivedFromClassA) classAObject;
}

In other words, the result will either be a null reference, or a reference to the same object, but statically typed to be of the derived type.

Upvotes: 6

Simon Steele
Simon Steele

Reputation: 11608

No, it's accessing the same object, but you now have access to the parts of that object from type DerivedFromClassA. There is only one object.

Additionally, if classAObject is not an instance of DerivedFromClassA or a type derived from it, then derivedObject will be null, as there's no valid cast.

Upvotes: 3

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