[fpc-devel] Re: [fpc-l] type discussion
Michael Van Canneyt
michael at freepascal.org
Thu Jun 2 17:28:32 CEST 2005
On Thu, 2 Jun 2005, Sebastian Kaliszewski wrote:
> Michael Van Canneyt wrote:
>> This is only 'logical' if the hypothesis
>> "productivity is inversely related to the syntax verbosity"
>> is correct.
> And it's not.
> What is correct is "productivity is directly related to the number of
> separate language constructs developer has to put in program to acomplish the
Inversely related, I assume you want to say :-)
> So, for example, need to put separate finally block to free memory means
> additional few constructs. Or lack of standard libary supplied container
> apropriate for a task requires programmer to develop his/her own or to adapt
> something less usable.
> Geeintg rid of end in begin / end wont help much (as they can;t be separated,
> they count as single construct).
> So here is some little idea which seems to me Pascalish enough to be
> how about new keyword: local
> Class variable declared local will be automatically freed upon every exit
> from the scope (i.e. something along the lines of implicit try/finally for
> some builtin types).
While I can see the use, there are all kinds of problems associated with it.
So instead of
S : TStringList;
ManagedVar // or whatever. All that goes here is freed again by the compiler.
S : TStringList;
// code here
end; // Compiler frees S here.
But the compiler needs to check many things:
1. Initialize the S with Nil.
2. Check that S is assigned only once during the lifetime of the
This is actually a bigger restriction than you might think,
unless you want to introduce reference counting.
3. Put a try/finally block and generate a call to S.Destroy at the end.
It must also catch any errors that may occur when s.destroy is
called. For classes, this danger is very real; For ansistrings it is
not (well, very small)
4. It cannot assign S to anything, since that could mean that the
lifetime of S could be prolonged. The alternative is again again ref. counting.
This is not so easy, and reference counting is always a mess...
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