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I tend to forget there is a record intialiser TPair.Create(Key, Value) – via: delphi – TDictionary populated during create example code – Stack Overflow

Posted by jpluimers on 2018/09/18

I tend to forget that since TPair – introduced in Delphi 2009 – has had a TPair.Create(Key, Value)record initialiser since Delphi 2010, though only fully documented since Delphi XE4:

With some spart short methods, Cosmin Prund shows a really nice helper at [WayBack] delphi – TDictionary populated during create example code – Stack Overflow allowing a call like this:

  with TDictHelper<Integer, string> do
    Dict := Make([P(1, 'one'), P(2, 'two')]);

His answer has all the details (including describing the pros and conse), so here is only the helper:

uses
  SysUtils, Generics.Collections;

type
  TDictHelper<Key, Value> = class
  public
    class function P(const K:Key; const V:Value): TPair<Key, Value>;
    class function Make(init: array of TPair<Key, Value>): TDictionary<Key, Value>;overload;
    class function Make(KeyArray: array of Key; ValueArray: array of Value): TDictionary<Key, Value>;overload;
  end;

{ TDictHelper<Key, Value> }

class function TDictHelper<Key, Value>.Make(init: array of TPair<Key, Value>): TDictionary<Key, Value>;
var P: TPair<Key, Value>;
begin
  Result := TDictionary<Key, Value>.Create;
  for P in init do
    Result.AddOrSetValue(P.Key, P.Value);
end;

class function TDictHelper<Key, Value>.Make(KeyArray: array of Key;
  ValueArray: array of Value): TDictionary<Key, Value>;
var i:Integer;
begin
  if Length(KeyArray) <> Length(ValueArray) then
    raise Exception.Create('Number of keys does not match number of values.');
  Result := TDictionary<Key, Value>.Create;
  for i:=0 to High(KeyArray) do
    Result.AddOrSetValue(KeyArray[i], ValueArray[i]);
end;

class function TDictHelper<Key, Value>.P(const K: Key;
  const V: Value): TPair<Key, Value>;
begin
  Result := TPair<Key, Value>.Create(K, V);
end;

–jeroen

7 Responses to “I tend to forget there is a record intialiser TPair.Create(Key, Value) – via: delphi – TDictionary populated during create example code – Stack Overflow”

  1. rvelthuis said

    Why is this not a class helper for TDictionary? Then you can do: Dict := TDictionary.Make(etc...);.

  2. sglienke said

    … in the meanwhile in .NET: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/how-to-initialize-a-dictionary-with-a-collection-initializer

    • rvelthuis said

      Wow, just like in Objective-C. They got that syntax a few years ago.

    • jpluimers said

      Cool!

      class StudentName
      {
          public string FirstName { get; set; }
          public string LastName { get; set; }
          public int ID { get; set; }
      }
      
      class CollInit
      {
          Dictionary students = new Dictionary()
          {
              { 111, new StudentName {FirstName="Sachin", LastName="Karnik", ID=211}},
              { 112, new StudentName {FirstName="Dina", LastName="Salimzianova", ID=317}},
              { 113, new StudentName {FirstName="Andy", LastName="Ruth", ID=198}}
          };
      }
      

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