Delphi basic tutorial graphic version of compound data types (collection)

In pascal, a set is composed of a set of data elements with the same ordered type . This ordered type is called the base type of the set.

Some people think that the collections in Delphi are useless. These people include myself, but in fact they are not. It also has many application scenarios. For example, in the past, many elements were always taken out of the database in the program, and then judged one by one. Now using collections can completely avoid this operation

Definition and description

Basic syntax: set of base type;

The base type can be any order type, but cannot be a real type or other structure type. At the same time, the sequence number of the base type data must not exceed 255 . Because the subrange type and the enumeration type are both ordered, they can be used together, as follows:

function IsContainCharacter(Character: Char): Boolean;
var
  Chars: set of 'A' .. 'Z';

begin
  Result := Character in Chars;
end;

begin
  try
    Writeln(IsContainCharacter('B'));
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;

  Readln;

end.

Note: Because the number of elements in the set does not exceed 256, var s:set of integer; is wrong.

Element traversal

procedure ListCharacters();
var
  Chars: set of char;
  Str: string;
begin
  Chars := ['A' .. 'J', 'a', 'm'];

  for var C in Chars do begin
    Str := Str + C;
  end;

  Writeln(Str);
end;

begin
  ListCharacters;
  Readln;
end.

Other operations

type
  TEnum = (One, Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten);
  TSetEnum = set of TEnum;

//初始化
procedure TForm4.Button3Click(Sender: TObject);
begin
  SetEnum  :=  [one, Two];
  SetEnum1 := [Three, Nine, Ten]
end;
//集合减少
procedure TForm4.Button5Click(Sender: TObject);
begin
  SetEnum := SetEnum - [Two];
end;
//集合增加
procedure TForm4.Button6Click(Sender: TObject);
begin
  SetEnum := SetEnum + [Three];
end;
//集合减少
procedure TForm4.Button7Click(Sender: TObject);
begin
  Exclude(SetEnum, One);
end;
//集合增加
procedure TForm4.Button4Click(Sender: TObject);
begin
  Include(SetEnum, Four);
  Include(SetEnum, Ten);
end;

Although the operation of the collection elements can be achieved through the +-symbol, the recommended usage is to use Include and Exclude as much as possible.