Null references (oh no, not again!)

[Sean Kelly]

Walter Bright wrote:
> Sean Kelly wrote:
>> In a language like Java where basically every variable is a reference, 
>> it can be a lot more difficult to figure out where a null came from. 
>> I've never had this problem in code I've written either, but I've had 
>> to maintain some Java code that was nearly impenetrable and this was 
>> absolutely an issue.
> 
> I've found that variables are rarely written to, but often read. A grep 
> finds the handful of places where it is written to (a good IDE should 
> also provide this information much better than grep). There just won't 
> be that many places to look.

Say one variable is initialized at 4 points by different variables, some 
are the same type and some are different types with an explicit 
downcast.  Now I have to consider a possible cast failure (the easy 
case) and I also have to look to see where those 4 variables were 
initialized, possibly introducing another 4 initialization points per 
variable, and so on.  It's entirely possible to do this, but I'm looking 
at either inserting checks at an exponential number of locations and 
then running once, or running and finding the offending initialization 
then running again to find the preceding offending initialization, etc. 
  Even worse is when a container is involved, since they tend to have a 
ton more points in the code where their contents are being altered or 
rearranged.

There's one instance in a Java program I've worked on where I've seen a 
variable be null that, from code inspection, should logically never be 
null at that point.  I'm sure I missed something subtle, but I'll be 
darned if I know what it is.

This is drastically different from a C/C++ application where references 
are the exception rather than the norm.  D stands somewhere between the 
two depending on programming style.

> (I tend to use grep a lot on code, and so tend to write variable names 
> that are amenable to grep. If you use globals named "i", hope you have a 
> decent IDE!)

Same here.  Without find/grep I'd have given up on programming long ago.