Delphi - Implicit typecast operator not working for method parameters

Question

I'm writing a kind of array wrapper, using a record as container, and including some "class-like" functions to it. I also want the possibility to assign an array to it, as with a normal array, so I have implemented a Implicit class operator:

type
  TArrayWrapper = record
    class operator Implicit(AArray: array of TObject): TArrayWrapper; overload;
    Items: TArray<TObject>;

    procedure Add(AItem: TObject);
    ...
  end;

So I can do things like:

procedure DoSomething;
var
  myArray: TArrayWrapper;
begin
  myArray := [Obj1, Obj2, Obj3];
  ...
end;

The problem appears when I try to pass an array of Integer to a method that has as parameter a TArrayWrapper:

procedure DoSomethingElse(AArrayWrapper: TArrayWrapper);
begin
    ...
end;


procedure DoSomething;
var
  myArray: TArrayWrapper;
begin
  myArray := [Obj1, Obj2, Obj3];
  DoSomethingElse(myArray);   <--- Works!!!!

  DoSomethingElse([Obj1, Obj2, Obj3]); <--- Error E2001: Ordinal type required -> It is considering it like a set, not as an array
end;

What could be happening?

Thank you in advance.

That's a compiler deficiency

Stefan Glienke
– Stefan Glienke

2019-05-30 11:47:29 +00:00
Commented May 30, 2019 at 11:47 — Stefan Glienke
– Stefan Glienke, Commented May 30, 2019 at 11:47

LU RD · Accepted Answer · 2019-05-31 08:56:02Z

4

The compiler has not implemented the string like operations on a dynamic array for class operators, when the record/class is used as a parameter.

~~There is not a QP report for this, as far as I can see.~~ Now there is, see below.

A similar example is found in the comments here: Dynamic Arrays in Delphi XE7

A workaround:

DoSomethingElse(TArray<TObject>.Create(Obj1, Obj2, Obj3));

Or as @Stefan suggests, in order to avoid unnecessary allocations. Add a constructor to the record:

type
  TArrayWrapper = record
    class operator Implicit(AArray: array of TObject): TArrayWrapper; 
    constructor Init( const AArray: array of TObject);
  end;

DoSomethingElse(TArrayWrapper.Init([obj1,obj2,obj3]));

Reported as: RSP-24610 Class operators do not accept dynamic arrays passed with brackets

edited May 31, 2019 at 8:56

answered May 30, 2019 at 11:50

LU RD

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3 Comments

Stefan Glienke Over a year ago

As a workaround I would rather suggest adding a ctor for the TArrayWrapper type with an array of TObject parameter than going through immediate dynamic array allocation and implicit operator call plus compiler added CopyRecord

LU RD Over a year ago

@StefanGlienke, thanks. Added your suggestion to the answer. I will report this to QP later today.

Leon Over a year ago

I was already using this solution. The code is less elegant than just passing the array, but It works. Thank you very much.

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