What does Coverity/clang static analysis actually do?

[Christopher Wright]

Nick Sabalausky wrote:
> static void Main(string[] args)
> {
>     Foo f;
>     if(args.Count() > 2) { f = new Foo(); }
> 
>     if(args.Count() > 2)
>     {
>        f.bar(); // ERROR: Use of unassgned local variable 'f'
>     }
> 
>     Foo f2;
>     createFoo(ref f2); // ERROR: Use of unassgned local variable 'f2'
>     f2.bar();
> }
> 
> static void createFoo(ref Foo f)
> {
>     f = new Foo();
> }
> ---------------------------------------------
> 
> The first one is rather strange coding though and makes it easy to hide 
> errors anyway. And the second one's a tad odd too, plus I don't see any harm 
> in solving that with "Foo f2=null": it would at least be a hell of a lot 
> better than the compiler doing that very same "=null" automatically. I know 
> Walter doesn't agree, but I'd much rather have a few slightly inconvinient 
> false positives (or would it really be a false negative?) than even a mere 
> possibility for a hidden error.

The second one is an error; createFoo might use its argument before 
assigning. You should have marked its argument as out instead, which 
would not yield an error.

In point of fact, that's a common pattern in C#. Dictionaries define a 
method bool TryGetValue(key, out value):

DateTime date;
if (dict.TryGetValue("key", out date))
{
     // use date
}