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fxcop

Why does FxCop think initializing fields to the default value is bad?

When assigning a default default-value to a field (here false to a bool), FxCop says:

Resolution   : "'Bar.Bar()' initializes field 'Bar.foo' 
               of type 'bool' to false. Remove this initialization 
               because it will be done automatically by the runtime."

Now, I know that code as int a = 0 or bool ok = false is introducing some redundancy, but to me it seems a very, very good code-practice, one that my teachers insisted on righteously in my opinion.

Not only is the performance penalty very little, more importantly: relying on the default is relying on the knowledge of each programmer ever to use a piece of code, on every datatype that comes with a default. (DateTime?)

Seriously, I think this is very strange: the very program that should protect you from making all too obvious mistakes, is suggesting here to make one, only for some increased performance? (we're talking about initialization code here, only executed once! Programmers who care that much, can of course omit the initialization (and should probably use C or assembler :-) ).

Is FxCop making an obvious mistake here, or is there more to it?

Two updates :

  1. This is not just my opinion, but what I have been taught at university (Belgium). Not that I like to use an argumentum ad verecundiam, but just to show that it isn't just my opinion. And concerning that:

  2. My apologies, I just found this one:

    Should I always/ever/never initialize object fields to default values?

Solution

  • There can be significant performance benefits from this, in some cases. For details, see this CodeProject article.

    The main issue is that it is unnecessary in C#. In C++, things are different, so many professors teach that you should always initialize. The way the objects are initialized has changed in .NET.

    In .NET, objects are always initialized when constructed. If you add an initializer, it's possible (typical) that you cause a double initialization of your variables. This happens whether you initialize them in the constructor or inline.

    In addition, since initialization is unnecessary in .NET (it always happens, even if you don't explicitly say to initialize to the default), adding an initializer suggests, from a readability standpoint, that you are trying to add code that has a function. Every piece of code should have a purpose, or be removed if unnecessary. The "extra" code, even if it was harmless, suggests that it is there for a reason, which reduces maintainability.