WST: Illegal type conversion: "new_record" to "Pointer" in generated
binder
lazarus / 38-Networking and Web Programming

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tom.tom · 2013-05-09 14:09

hi,

I'm working on my SOAP web service and have come across following
issue:

when in an interface the simple record type is defined as follows:

Code: [Select]  new_record = record
    test : string;
  end; 

and it is used as an input parameter to some web method - i.e.

Code: [Select]    procedure new_proc(
      const  AValue : new_record
    );

then in the binder, the following autogenerated code works fine:

Code: [Select]procedure
TSampleService_ServiceBinder.new_procHandler(AFormatter :
IFormatterResponse; AContext : ICallContext);
var
  (...)
  AValue : new_record;
begin
  callCtx := AContext;
  Fillchar(AValue,SizeOf(new_record),#0);
 
  locStrPrmName := 'AValue'; 
AFormatter.Get(TypeInfo(new_record),locStrPrmName,AValue);
  if ( PTypeInfo(TypeInfo(new_record))^.Kind = tkClass ) and
Assigned(Pointer(AValue)) then
    callCtx.AddObjectToFree(TObject(AValue));

but if I change the definition of the record to:

Code: [Select]  new_record = record
    test : string;
    test2 : string;
  end;    

then the compilation fails in a binder on line:

Code: [Select]  if ( PTypeInfo(TypeInfo(new_record))^.Kind = tkClass )
and Assigned(Pointer(AValue)) then

with message:

Code: [Select]  Error: Illegal type conversion: "new_record" to
"Pointer"

I'm not an expert in OP internals and how the record vs. class
structures are handled, so could anybody please explain what is
happening?

Is it because if inside the record there is only one field the record
is treated as if it was directly that field (string in this case)
which can be casted to Pointer but if there are more fields it cannot
be casted since it is not a pointer...?

Cheers,
Tom

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Dibo · 2013-05-09 15:10

Last time when I worked on SOAP and WST was a 3 years ago, but what I
remember you  should not change autogenerated types manually. However
if you must, then you need change it everywhere (especially in wst
file definition). I'm pretty sure that in some other file generated by
WST exists old definition of new_record

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User137 · 2013-05-09 18:45

If it's put down to this piece:
Code: [Select]var AValue : new_record;
...
if Assigned(Pointer(AValue)) then1) AValue will never be nil because
it's variable.
( 2) i think it should be Assigned(@AValue), if you were to write it
like that. )
3) You cannot typecast a record into generic class object with
TObject(AValue).

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taazz · 2013-05-10 06:09

The code shown here is base on the short circuit Boolean evaluation,
this means that if the first part of the expression is false the
second part should not be evaluated. In your case if FPC supports
short circuit evaluation it should not make any difference. By the
error I assume that it does not.

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tom.tom · 2013-05-10 12:45

@Dibo: it does not matter if I manually modify the record or add a new
property using WST wizard - the result is the same

@User137, @taazz: this fails on COMPILATION not at runtime

So, this means there is apparently a bug in WST autogenerated code as
it also looks bizzare to me that the record type is being checked and
casted like an object. Now I'm wondering how come that such an obvious
issie has not been fixed yet... or maybe I'm doing something wrong...
or maybe the record types should not be used as input params in WST?