[fpc-pascal] Weird interface behavior

[Michael Van Canneyt]

On Sun, 23 Jan 2011, leledumbo wrote:

>
> WARNING: it won't be simple
>
> I'm using visitor pattern in my project and to the best of my knowledge, the
> visitor should be implemented as an interface.

Why ? 
tiOPF uses the visitor pattern extensively, and it is implemented as a class.

> After everything goes
> compiled, I found out a weird behavior. That is, all the change during
> accept-visit is gone after control goes back to the initiator (first
> accept). Even worse, I can't free the object! It causes access violation.
>
> I attach the project that shows this. The project is quite big, but you can
> focus to only two units (more precisely, to their interface as seen in the
> attached diff): ast and cg. I create two versions of both units (the other
> using class with abstract methods) and their diff is attached. Try compiling
> with both versions (by renaming the one you want to compile to the right
> name, e.g. without .tmp suffix). Ensure linguc.lpr on line 118 is commented
> when you're using the interface version (it causes access violation as I
> state above).
>
> Attachment:
> http://free-pascal-general.1045716.n5.nabble.com/file/n3353651/intf.zip
> intf.zip

It doesn't compile for me. What version of FPC did you use ?

home: >fpc linguc.lpr 
ast.pp(529,19) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTVarDecl"
ast.pp(531,15) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTStatement"
ast.pp(540,19) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTVarDecl"
ast.pp(542,15) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTStatement"
ast.pp(568,16) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTVarDecl"
ast.pp(623,15) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTMethod"
ast.pp(632,15) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTMethod"
ast.pp(651,14) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTClass"
ast.pp(659,14) Error: Cannot find an enumerator for the type "TFPGObjectList$TASTClass"
ast.pp(676) Fatal: There were 9 errors compiling module, stopping
Fatal: Compilation aborted
Error: /usr/local/bin/ppcx64 returned an error exitcode (normal if you did not specify a source file to be compiled)

Michael.