It's previously been pointed out to me that a declaration such as

     procedure OutputWriteF(const str: widestring; values: array of
const; fg: TColor= clBlack; bg: TColor= clDefault);

can't be rewritten

type owfArray: array of const;
     procedure OutputWriteF(const str: widestring; values: owfArray; fg:
TColor= clBlack; bg: TColor= clDefault);

since this would make the parameter into a dynamic rather than an open array. I'm entirely happy to accept that now that I understand it.

However, given a declaration of that form, is it possible to define a default parameter of [] so that OutputWriteF('Test, no params\n') is valid?

However, given a declaration of that form, is it possible to define a default parameter of [] so that OutputWriteF('Test, no params\n') is valid?

Not for open arrays, but you can write an overloaded version without the open array argument that calls the version with the open array parameter passing an empty array, or an array initialised with whatever "default" values you want:

interface
procedure OutputWriteF(const str: widestring); overload;
procedure OutputWriteF(const str: widestring; values: array of const); overload;
implementation
procedure OutputWriteF(const str: widestring);
begin
  OutputWriteF(str, [clBlack, clDefault]);
end;
procedure OutputWriteF(const str: widestring; values: array of const);
begin
 ...
end;

HTH

Constantine.

Thanks, good point and adequate workaround.