[fpc-devel] [] property overloads

[Ondrej Pokorny]

On 02.07.2019 08:17, Michael Van Canneyt wrote:
> On Tue, 2 Jul 2019, Ondrej Pokorny wrote:
>> I happened to study this part of FPC code back in 2015 when I worked 
>> on issue #28820. I can say that FPC directly transfers indexed 
>> properties
>
> Stop... How does FPC decide it is an indexed property ?

First of all I have to correct my notation (because I now re-checked FPC 
sources).

"Indexed property" from FPC POV is a property with an index defined ( 
https://www.freepascal.org/docs-html/ref/refsu34.html ):
property X : Longint index 1 read GetCoord Write SetCoord;
- the property above is referred to as "indexed property" in FPC source 
comments and it has the ppo_indexed option in tpropertyoptions.

Delphi documentation understands with "indexed property" the "array 
property" - see 
http://docwiki.embarcadero.com/RADStudio/Rio/en/Properties_(Delphi) 
"Array properties are indexed properties":
property Objects[Index: Integer]: TObject read GetObject write SetObject;

I will now use the notation "array property" instead of the ambiguous 
"indexed property".

---

Q: How does FPC decide it is an array property ?

This is simple. If the compiler encounters

MyTest.StringArray

it looks into the symtable. If a property is found (tpropertysym), it 
calls the "compiler property handler procedure" handle_propertysym.
See
procedure handle_propertysym(propsym : tpropertysym;st : TSymtable;var 
p1 : tnode);
in in pexpr.pas.

handle_propertysym checks if it is an array property (ppo_hasparameters 
in tpropertysym.propoptions) - in this case the compiler expects some 
parameters (even empty parameters are allowed) - see that the 
"try_to_consume(_LECKKLAMMER)"=false result is silently ignored and also 
it is not checked if paras are empty.

The compiler passes then the "paras" parameters to the getter/setter 
call (that automatically searches for a valid method overload with the 
used parameters).

Ondrej