Error: Generics without specialization cannot be used as a type for a variable

[dmitryb]

Hello

Why I am getting a compilation error?

Error: Generics without specialization cannot be used as a type for a variable

In Delphi, this file compiles without errors.

Code: Pascal  [Select][+][-]

1. type
2.   TBaseRowViewEh = class;
3.   TBaseFieldViewEh = class;
4.   TBaseTableLinkEh = class;
5. ...
6.  
7.   TFieldViewListEh = class(TEnumerable<TBaseFieldViewEh>)
8.   private
9. ...

[bytebites]

Use {$mode delphi} or with {$mode objfpc} specialize 

Code: Pascal  [Select][+][-]

1. TFieldViewListEh = class(specialize TEnumerable<TBaseFieldViewEh>)

[paweld]

The ObjFPC mode (which is the default in Lazarus if the mode is not explicitly specified) requires specialization for generics.
So you must add the specialize keyword for each generic type ( https://www.freepascal.org/docs-html/ref/refse54.html ), or force the Delphi mode in the unit header, eg.

Code: Pascal  [Select][+][-]

1. unit MyUnit;
2. {$mode delphi}
3. //....
4.  
5.  
6.  

[dmitryb]

The documentation for {$mode delphi} does not contain information about compilation mode changes relative to the reserved word `specialized`.

https://www.freepascal.org/docs-html/3.2.0/prog/progse74.html

Is there a complete description of {$mode delphi}?

[paweld]

because Delphi mode does not require specialization the spetialize keyword.
And the module you're showing doesn't have Delphi mode set, that's why you get an error about no specialization.
Modify this unit as follows and you should not have the error:

Code: Pascal  [Select][+][-]

1. unit EhLib.TableLinks;
2.  
3. {$mode delphi}
4.  
5. interface
6.  
7. uses
8.  
9. //rest of code
10.  

[PascalDragon]

Is there a complete description of {$mode delphi}?

The Delphi manuals.

because Delphi mode does not require specialization.

Please use the correct terms. Specialization is required no matter the mode and which is what [specialize] Identifier<Type[, Type[, …]]> does. What is not used in mode Delphi are the generic and specialize keywords.

[paweld]

Please use the correct terms. Specialization is required no matter the mode and which is what [specialize] Identifier<Type[, Type[, …]]> does. What is not used in mode Delphi are the generic and specialize keywords.

Thank you for the clarification