Question

A colleague of mine and I have been discussing how to declare variables in a function.

Let’s say you have a class called TStrings (using Delphi for the sake of explanation) that has at least one abstract method and a descendant class called TStringList which obviously implements the abstract method, but it introduces nothing else you need that is not already implemented in the ancestor, how would you declare a function variable of type TStringList?

Here are two examples. Which is considered better practice and why?

procedure AddElements; var   aList: TStringList; begin   aList := TStringList.Create;   try     aList.Add('Apple');     aList.Add('Pear');   finally     aList.free;   end; end;  procedure AddElementsII; var   aList: TStrings; begin   aList := TStringList.Create;   try     aList.Add('Apple');     aList.Add('Pear');   finally     aList.free;   end; end; 

Answer 1

It is a TStringList, so you should also declare it as TStringList (first example). Everything else could confuse you or others that read the code later.