Clear a TList or a TObjectList

Question

I\'m a bit puzzled of what to use for storing objects in a list. Until now I have used TList and freed each item in a loop. Then I discovered TObjectList

Answer 1

1. TList won't free the elements, with both Clear or Free.

aList.Clear;

Will just set aList.Count := 0 without freeing the aList.Items[] elements. So you'll leak memory. You'll need an explicit free as such:

for i := 0 to aList.Count-1 do
  TObject(aList[i]).Free;

But this is what TObjectList does... :)

About TObjectList, it is worth saying that TObjectList.Destroy is calling Clear.

So

aObjectList.Clear;
aObjectList.Free;

is exactly the same as

aObjectList.Free;

2. To store a list of records, you can use a dynamic array.

You'll get all TList methods (and more) with our dynamic array wrapper. That is, Add / Delete / Clear / Count / IndexOf / Find...

It has built-in serialization features (in binary or JSON), automated sorting and comparison (using RTTI) which are not existing with a TList/TObjectList. From Delphi 5 and later.

With more modern version of Delphi, you may use generics to handle the dynamic array, if you do not want to use a third-party library.