Delphi record operator for static arrays

Question

Is there a way to make something like this work?

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

type
  TMyRecord = record
    class operator Explicit(const a: array of integer): TMyRecord;
  end;

{ TMyRecord }

class operator TMyRecord.Explicit(const a: array of integer): TMyRecord;
begin
end;

var
  a: array[0..100] of integer;
begin
  TMyRecord(a);  //Incompatible types: 'array of Integer' and 'array[0..100] of Integer
end.

"TMyRecord.Explicit(const a: TIntegerDynArray)" works for TIntegerDynArray, but I can't get static arrays to work.

Ken White · Accepted Answer · 2012-05-10 22:20:36Z

3

It works (well, compiles ) if you declare your static array as a type:

program Project1;

{$APPTYPE CONSOLE}

uses
  System.SysUtils;

type 
  TMyArray = array[0..100] of Integer;  

  TMyRecord = record 
    class operator Explicit(const a: TMyArray): TMyRecord; 
  end; 

class operator TMyRecord.Explicit(const a: TMyArray): TMyRecord; 
begin 
end; 

var 
  a: TMyArray; 

begin 
  TMyRecord(a); 
end;

end.

answered May 10, 2012 at 22:20

Ken White

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1 Comment

Giel Over a year ago

Thanks, but in our case the arrays can have different sizes.

David Heffernan · Accepted Answer · 2012-05-10 20:11:37Z

2

I'd say that is a compiler bug/limitation and that you have no way around it.

I tried using Slice like this:

TMyRecord(Slice(a, Length(a)));

which results in this compiler error:

E2193 Slice standard function only allowed as open array argument

So the compiler doesn't recognise that the explicit operator is expecting an open array parameter.

A plain method call rather than an operator is fine which further leads me to believe that the compiler is simply not going to play ball.

If you can't use open arrays then there is no clean way out for you.

answered May 10, 2012 at 20:11

David Heffernan

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Comments

PatrickvL · Accepted Answer · 2012-05-11 09:00:34Z

0

An alternative is to cast to a pointer-type via the address of the variable :

type 
  PMyRecord = ^TMyRecord;

// ...

begin
  PMyRecord(@a).DoWhatever;
end;

answered May 11, 2012 at 9:00

PatrickvL

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