[fpc-pascal] Pre-allocated TFPGList or similar

[Sven Barth]

Am 24.11.2019 um 10:14 schrieb Michael Van Canneyt:
>
>
> On Sun, 24 Nov 2019, Sven Barth via fpc-pascal wrote:
>
>> Am 23.11.2019 um 23:42 schrieb Ryan Joseph via fpc-pascal:
>>> I need a pre-grown list which I can put (not insert!) items into at 
>>> indexes 
>> without getting "List index out of bounds" errors. For example I want 
>> to start with a list that has 10 empty indexes:
>>>
>>> list := TList.Create(10); // 10 empty slots!
>>>
>>> list[5] := someItem;
>>>
>>> Is this possible using any list type in the RTL? Actually I'd rather 
>>> just 
>> disable all the out of bounds errors because  I need some performant 
>> which isn't making more checks than need be. I want to use a 
>> heap-based list because the it may need to grow later.
>> What you're looking for is the Count property. Setting it is 
>> supported by the untyped lists in Classes, the generic ones in FGL as 
>> well as those in Generics.Collections.
>
> Better yet, use Capacity.
>
> Count is meant to set the number of slots actually used.
> Capacity is the number of allocated slots.
But the setter for the items checks against Count, not Capacity, so the 
code I showed will fail if used with Capacity instead of Count. At least 
both properties should be set to work correctly.

Regards,
Sven