Records as TDictionary keys

[balabuev 102]

Did you know that the following will automatically work with TDictionary:

type
  TMyKey = record
  public
    class operator Equal(const A, B: TMyKey): Boolean;
    function GetHashCode: Integer;
  end;

Without the need to write custom equality comparer. At least in Delphi 12 it works. And System.TypeIfo unit contains GetRecCompareAddrs function, which is used in default equality comparer implementation. I realized it only recently, and see no docs/info on the internet.

[pyscripter 689]

Just keep in mind [RSP-43423] Using {$WEAKLINKRTTI ON} causes access violation on TList<T>.IndexOf method - Embarcadero Technologies,

See also 

 

Edited June 24 by pyscripter

[A.M. Hoornweg 144]

15 hours ago, balabuev said:

Did you know that the following will automatically work with TDictionary:

type
  TMyKey = record
  public
    class operator Equal(const A, B: TMyKey): Boolean;
    function GetHashCode: Integer;
  end;

Without the need to write custom equality comparer. At least in Delphi 12 it works. And System.TypeIfo unit contains GetRecCompareAddrs function, which is used in default equality comparer implementation. I realized it only recently, and see no docs/info on the internet.

 

Hey, that's actually really cool!

 

[Sisko 0]

It's cool BUT it's also very slow.

 

see https://embt.atlassian.net/servicedesk/customer/portal/1/RSS-886

A generic list takes 100x longer to be generated than before (Delphi 11.3)

[Der schöne Günther 316]

It it sufficient to have an equality operator or is the GetHashCode(): Integer method needed as well?

[Stefan Glienke 2002]

Of course - TDictionary<K,V> is hashtable based, so it needs GetHashCode and Equals

[pyscripter 689]

 

On 6/24/2024 at 6:28 PM, balabuev said:

Did you know that the following will automatically work with TDictionary:

This will no longer work by default in Delphi 12.2.

You would need to add to your code:

  System.TypInfo.GetRecCompareAddrs := System.TypInfo.GetRecordCompareAddrs;

 

Also using {$WEAKLINKRTTI ON} no longer causes crashes.   It just results in using the default equality and GetHashCode functions.