Re: What would you like in Ada202X?

[sbelmont700@gmail.com]

On Sunday, April 29, 2012 7:29:24 PM UTC-4, Shark8 wrote:
> In all likelihood an auto-deallocate would be an null procedure which is extended by the other classes. (i.e. doing what we've described, but in this case hidden from the programmer.)
> 

The auto-deallocate scheme I was refering to is to remove the 'free' procedure entirely.  Whenever the object is finalized (by the language, not user-defined finalization), all the elements of the record will be finalized as well.  So the concrete type that contains some sort of Auto_Deallocated_File_Pointer type (that is, itself, controlled) would close the file pointer automatically, and concrete types that contain nothing would do just that.  Free doesn't exist, and certainly isn't null.

Generally I have found that schemes that rely on explictly calling deallocation routines are rarely, if ever, exception safe and normally tend to produce memory leaks.  If you have to deallocate 'n' items and an exception is raised after item 'x', then you leak the memory for n-x items (or have incomprehensible sets of nested exception handlers).  But this is beside the point.

> That's just it though. Thing like the free/deallocate mentioned ARE valid for all types in that class-hierarchy, it's just that (even as you admitted) sometimes it's a NOP.
> 

Having nothing to do is not the same as it having been done, and that's a dangerous philosophy to adhere to.  Free is not valid for a type if there is nothing to free, and extending landing gear is not valid for a plane with fixed gear.  If you were using a straight procedural model (without inheritance), would you go to all the trouble of creating a Free procedure without any code and calling it to accomplish nothing?  Trying to fake a common interface does not make for an abstract program.