[fpc-pascal] dynamic array contents and system.move

ajv info at vogelaar-electronics.com
Tue Apr 27 08:22:58 CEST 2010


I dit not follow this thread, but maybe it helps.
Dynamic arrays are located on the heap  and are reference counted.
The command System.Move will bypass the reference counting.
For this reason and to be sure the data is available when you need it 
use System.Move on stack located arrays an strings only.


On 04/27/2010 08:04 AM, J├╝rgen Hestermann wrote:
>>>>> There is a lot of ambigouity with dynamic arrays.
>>>> There certainly is if you expect them to work like regular arrays. 
>>>> They are a quite different datatype.
>>> At least it should always mean the same independent from context.
>> It does always mean the same, just like a class instance always means 
>> the same. It's just that implicit dereferencing is applied as soon as 
>> you try to access an element (again, like with classes).
>
> That means that identifiers for open arrays are always pointers, 
> 'just' with an automatic dereferencing when using square brackets for 
> indexing? Then it should be possible to dereference such identifiers 
> with ^ but it's not. Why? That's the inconcistency I mean: There is no 
> strict logic behind it.
>
> An identifier should always refer to a memory address/location. If the 
> type of the data at that memory location is a pointer then it should 
> be possible to change the expression to the memory address of the data 
> by dereferencing it with ^. But for dynamic arrays (and AnsiStrings 
> and other "modern" structures) this is no longer the case which leads 
> to a lot of confusion. To me it's a design flaw.
> And the help does not tell about the internals (motto: "you don't need 
> to bother about the internals") but if someone follows this advice and 
> it does not work as expected then here in the list all say "don't use 
> it if you don't know about the internals". But then why not tell the 
> internals in the documentation? If I construct a heavily nested data 
> structure with records and pointers to records how do I know that 
> these "special" things like AnsiStrings etc. don't work as all the 
> other types that made the Pascal language so popular. It was clear and 
> easy to understand but now it is no longer.
>
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