[fpc-pascal] optional parameter

Martin fpc at mfriebe.de
Mon May 3 20:15:57 CEST 2010

On 03/05/2010 10:58, spir ☣ wrote:
> Hello,
> A few questions on the topic:
> * Is it possible to define an optional parameter without default value?
> * Is it at all possible for an optional *argument* not to be the last in actual call? Eg
>       procedure p(a:Integer=0 ; b:Integer=0)
>    How can the caller pass b and not a?
> * The ref states: "For dynamic arrays or other types that can be considered as equivalent to a pointer, the only possible default value is Nil."
> Does this apply to any non-atomic type? Which are the "other types that can be considered as equivalent to a pointer"?
> Tried with a record, but cannot make it be accepted by the compiler. Needed to change the parameter to be a pointer to the record instead (so the default can be nil), but this creates a trap for the calling code.
> Else, is there a common trick or workaround?

Maybe you want to use overloading instead of optioanl parameters?

Procedure Foo; overload; // no params
Procedure Foo(SomeRecord: TRecordType); overload; // no params

then of course you need to implement twice

Procedure Foo;
var a: TRecordType;
    a:= xxx;/your defaults

Procedure Foo(SomeRecord: TRecordType);
   / do work

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