Adding Append method to the generic TArray type

Question

I'm trying to add an Append method to the System.Generics.Collections.TArray type.

unit uMyArray;

interface

uses
  System.Generics.Collections;

type
  TArray = class(System.Generics.Collections.TArray)
  public
    class procedure Append<T>(var AValues: array of T; const AItem: T); static;
  end;

implementation

class procedure TArray.Append<T>(var AValues: array of T; const AItem: T);
begin
  SetLength(AValues, Length(AValues) + 1);
  AValues[Length(AValues) - 1] := AItem;
end;

end.

On compiling I get the following error on the SetLength line:

[dcc32 Error] uMyArray.pas(18): E2008 Incompatible types

Bit of an antipattern, this increase the length of the array by one. Can result in fragmented address space. — David Heffernan
– David Heffernan, Commented Apr 3, 2020 at 12:03
You shouldn't append one element at a time. See stackoverflow.com/a/5756206/282848 — Andreas Rejbrand
– Andreas Rejbrand, Commented Apr 3, 2020 at 12:05

David Heffernan · Accepted Answer · 2020-04-03 11:59:35Z

3

You cannot resize an open array parameter. You need to pass TArray<T>.

Change

class procedure Append<T>(var AValues: array of T; const AItem: T); static;

to

class procedure Append<T>(var AValues: TArray<T>; const AItem: T); static;

answered Apr 3, 2020 at 11:59

David Heffernan

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