[fpc-pascal] Generics vs templates

Graeme Geldenhuys mailinglists at geldenhuys.co.uk
Wed Jan 10 00:37:16 CET 2018

On 2018-01-09 01:29, Ryan Joseph wrote:
> What does this have to do with generics exactly?

Everything I guess. ;-) That was the point of my reply.

When using the Generics.Collections unit of Delphi I can define a list 
class that can hold Integer data types, by doing the following:

     IntList: TList<Integer>;
     IntList := TList<Integer>.Create;

How Generics does that (how it is implemented underneath), I don't know 
- I never bothered to look. All I'm saying is that in our company the 
developers love Generics, but then can't understand why performance 
degrades is some areas of our project. Further testing revealed that the 
usage of Generics was partly to blame.

I then investigated this, and compared some of those lists, and 
implementing the equivalent manually (using TList, TObjectList and 
such). For example, the above code example can be accomplish with a 
TList only.

     IntList: TList;
     IntList := TList.Create;

Yes, the second code sample might not look so nice (the casting), but it 
was just the simplest and quickest example I could knock up to store 
integers in a list. Either way, the non-Generics code example was 
considerably faster in adding and freeing itself.

This was just one example. TObjectList (or a customised descendant... 
eg: TAddressList) was another case where it was way faster than 
Generics.Collections.pas unit provided.

Like I said, this was all tested under Delphi XE3. I didn't have time 
today to test under FPC, but will try and do so tomorrow.


fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal

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