"If C# manipulates objects by reference, will a swap work?" - This issue must certainly have troubled quiet a lot of beginners. C# does manipulate objects by reference, and all object variables are references. On the other hand, C# does not pass method arguments by reference; it passes them by value, (even if the method arguments are of reference type). Thus, a regular swap method will not work! Let's come from the beginning, we know that there are four kinds of formal parameters in a C# method declaration, namely Value parameters, which are declared without any modifiers. (default) Reference parameters, which are declared with the ref modifier. Output parameters, which are declared with the out modifier. Parameter arrays, which are declared with the params modifier. Thus if there is no any method parameter keyword (ref or out), the parameter can have a value associated with it. That value can be changed in the method, but that value will not be reflected when the control passes back to the calling procedure. This is true for all value types. Now, consider a reference type, an object. If we pass an object to a method and if the value of its member is changed, it will be retained even when the control is passed back to the calling procedure! This is because objects are manipulated by reference. If so, then, if we pass two objects to a regular swap method and come back to the calling procedure to see whether they have got swapped, they would have not! Look down the code below,
The out put is as follows
In the above program, we pass the instances obj1 and obj2 of class1 to badswap_noref() method and see that they are not actually getting swapped. This is what actually happens in the badswap_noref method. Not the actual references obj1 and obj2 are passed. But a copy of the references is passed. So param1 and param2 contains a copy of the actual references obj1 and obj2 respectively. We are able to modify the values of X and Y in the badswap_noref method thru param1 and param2, because param1 and param2 still points to the same address locations referred to by obj1 and obj2. But what we are swapping is only param1 and param2, the method references, which are not retained when we come back to the calling procedure, Main().
Thus, in C#, a swap method can be made possible by using the ref keyword. In such a case, we pass the object references explicitly by reference and not by value, thus able to swap them right in the called method.
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