Question

When I write the following code in C#:

SqlCeCommand command;
try
{
    // The command used to affect the data
    command = new SqlCeCommand
                  { 
                     // init code removed for brevity
                  };

    // Do stuff 
    // Do more stuff
}
finally
{
    if (command != null)
        command.Dispose();
}

Resharper complains on my check of command != null. It says that command may not be assigned (because it could fail some how in the constructing and still hit the try block).

So I change the declaration of command to be SqlCeCommand command = null; and everyone is happy.

But I am left wondering what the difference is?

And why doesn’t it just default to null? Meaning: How does C# benefit from not just defaulting local variables to null?

Answer 1

Class field members get defaulted (value types each depending on its type, ref types to null) but local variables do not.

// Example 1:
SomeClass someObject;
if(x == y)
{
    someObject = new SomeClass();
}
someObject.someMethod();   //Error since it may not execute the if statements

// Example 2
SomeClass someObject;
someObject = new SomeClass();
someObject.someMethod();   //No Error

EDIT: This was designed to avoid C++ runtime errors which was causing the program to close unexpectedly (because of null pointers).

P.S: You may not downvote me when I talk about C# specs (I didn’t make C# specs, I cheer this avoidance though).