This is a common pattern I’m finding when working with generics in FPC. In the example below there is an equals comparison that needs to be checked but for some types such as records there is no default operator overload so I need to add one for every record that will be specialized in the class.

Is there a way around this? I’d like to just skip the comparison for specialized types that can’t be compared if possible.

type
	generic TCollection<T> = class
		procedure AddValue (value: T);
	end;
procedure TCollection.AddValue (value: T);
begin
	// comparison operator doesn't exist for records so I get compiler errors if I specialize TCollection with a record type
	if value = T then
		;
end;

Regards,
Ryan Joseph

"Ryan Joseph" wrote

This is a common pattern I’m finding when working with generics in FPC.

In the example below there is an equals comparison that needs to be checked but for some types such as records there is no default operator overload so I need to add one for every record that will be specialized in the class.

Is there a way around this? I’d like to just skip the comparison for

specialized types that can’t be compared if possible.

compiler errors if I specialize TCollection with a record type

if value = T then ; end;

You could try to use the TEqualityComparer (or so) types from the rtl-generics package (don't know in which unit exactly they are ^^') as those can work with records without operator overloads.

Regards,
Sven

On Sep 12, 2017, at 12:59 PM, Sven Barth via fpc-pascal wrote: You could try to use the TEqualityComparer (or so) types from the rtl-generics package (don't know in which unit exactly they are ^^') as those can work with records without operator overloads.

Do any examples of how to use the class exist? I searched around and couldn’t find a single snippet even though it appears to exist in Delphi.

Regards,
Ryan Joseph

2017-09-12 7:59 GMT+02:00 Sven Barth via fpc-pascal <

Generics.Defaults :P

2017-09-12 11:07 GMT+02:00 Ryan Joseph :

Do any examples of how to use the class exist? I searched around and couldn’t find a single snippet even though it appears to exist in Delphi.

Please check example at :
packages\rtl-generics\examples\tcomparer\tcomparerproject.lpr

On Sep 12, 2017, at 4:46 PM, Maciej Izak wrote: Please check example at : packages\rtl-generics\examples\tcomparer\tcomparerproject.lpr

Thanks. What is the & here? TCompare.&String(Left.Name, Right.Name);

I don’t think I’ve ever seen that before.

Regards,
Ryan Joseph

It means you use a language keyword as an identifier. An ugly habit, but unfortunately inherited from Delphi.

Originally intended to be able to create imports of other languages (think SOAP, COM) it is now of course abused...

Michael.