Code explanation

Question

Hi

Ive been looking inside the .NET Framework and have noticed a general pattern appearing.

Given the code below:-

public void Insert(object key, object value, bool add)

if(this.count >= this.loadsize)

My question is, the very first condition that is checked is by the if statement. But how are the fields count and loadsize initialized with values? is it when the actual instantiation of the method occurs?

Regards

Steven

Vulpes · Answer

As they're preceded by 'this' we can tell straightaway that 'count' and 'loadsize' are instance fields or properties of the class which contains the Insert method. These fields will have been initialized where they are defined or in the class's constructor. Otherwise they will have their default values depending on their type. So when an instance of the class is created its instance fields will be initialized one way or another.

S · Answer

Appreciated Vulpes thanks

Vulpes · Answer

That's right Steven. If you declare parallelOptions as a local variable rather than a parameter then the variable must be initialized so it refers to an actual object before you can use it. Notice also that unlike many other languages local variables don't have a default value (even null) in C#. You always have to assign something to them otherwise the compiler will complain that they haven't been initialized before use.

S · Answer

And I guess only in an if statement can the ParellelOptions instance be used like this otherwise the compiler will error with Object reference is not set to an Instance of an Object like if it was declared in the method body like so:- public static void Invoke() ParallelOptions parallelOptions; parallelOptions.CancellationToken.CanBeCancelled; The error occurs as the object instance has not yet been instantiated?

Vulpes · Answer

Well in that example a reference to a ParallelOptions instance is passed into the Invoke method and assigned to the parameter parallelOptions. So the code within the method body can use this instance in the 'if' statement - there's no need to create a new one. Incidentally the code should include a check that parallelOptions is not null otherwise a null reference exception will be thrown when the runtime attempts to access its CancellationToken property.

S · Answer

Hi Vulpes In the case of method parameters like the following:- (Shortened for simplicity) public static void Invoke(ParallelOptions parallelOptions) if(parallelOptions.CancellationToken.CanBeCancelled) throw new ArguementNullException(parallelOptions); Is it due to the fact the conditional if statement is in play allowing access to the parallelOptions variable without having to create an instance of ParallelOptions first in order to access its members? Regards Steven

S · Answer

Thanks Vulpes basics really.