delphi 中record 的类操作符重载简介

今天简单介绍一下 delphi 中record 的类操作符重载使用，就是如何 实现 record 之间的简单操作。

关于类操作符重载 ，大家可以看 官方的文档。

Delphi allows certain functions, or "operators", to be overloaded within record declarations. The name of the operator function maps to a symbolic representation in source code. For example, the Add operator maps to the + symbol.

The compiler generates a call to the appropriate overload, matching the context (that is, the return type, and type of parameters used in the call), to the signature of the operator function.

The following table shows the Delphi operators that can be overloaded:

Operator	Category	Declaration Signature	Symbol Mapping
Implicit	Conversion	Implicit(a : type) : resultType;	implicit typecast
Explicit	Conversion	Explicit(a: type) : resultType;	explicit typecast
Negative	Unary	Negative(a: type) : resultType;	-
Positive	Unary	Positive(a: type): resultType;	+
Inc	Unary	Inc(a: type) : resultType;	Inc
Dec	Unary	Dec(a: type): resultType	Dec
LogicalNot	Unary	LogicalNot(a: type): resultType;	not
Trunc	Unary	Trunc(a: type): resultType;	Trunc
Round	Unary	Round(a: type): resultType;	Round
In	Set	In(a: type; b: type) : Boolean;	in
Equal	Comparison	Equal(a: type; b: type) : Boolean;	=
NotEqual	Comparison	NotEqual(a: type; b: type): Boolean;	<>
GreaterThan	Comparison	GreaterThan(a: type; b: type) Boolean;	>
GreaterThanOrEqual	Comparison	GreaterThanOrEqual(a: type; b: type): Boolean;	>=
LessThan	Comparison	LessThan(a: type; b: type): Boolean;	<
LessThanOrEqual	Comparison	LessThanOrEqual(a: type; b: type): Boolean;	<=
Add	Binary	Add(a: type; b: type): resultType;	+
Subtract	Binary	Subtract(a: type; b: type) : resultType;	-
Multiply	Binary	Multiply(a: type; b: type) : resultType;	*
Divide	Binary	Divide(a: type; b: type) : resultType;	/
IntDivide	Binary	IntDivide(a: type; b: type): resultType;	div
Modulus	Binary	Modulus(a: type; b: type): resultType;	mod
LeftShift	Binary	LeftShift(a: type; b: type): resultType;	shl
RightShift	Binary	RightShift(a: type; b: type): resultType;	shr
LogicalAnd	Binary	LogicalAnd(a: type; b: type): resultType;	and
LogicalOr	Binary	LogicalOr(a: type; b: type): resultType;	or
LogicalXor	Binary	LogicalXor(a: type; b: type): resultType;	xor
BitwiseAnd	Binary	BitwiseAnd(a: type; b: type): resultType;	and
BitwiseOr	Binary	BitwiseOr(a: type; b: type): resultType;	or
BitwiseXor	Binary	BitwiseXor(a: type; b: type): resultType;	xor

No operators other than those listed in the table may be defined on a class or record.

以下是通过实例来演示

TXalionRec=record
   ival:integer;
   dval:Tdatetime;
   constructor create;
   destructor Destroy;

    class operator Assign(var Dest:TXalionRec;const Src:TXalionRec); // 赋值

    class operator NotEqual(ALeft,ARight:TXalionRec):boolean;  // 不等于
    class operator Equal(ALeft,ARight:TXalionRec):boolean;  //等于
    class operator GreaterThan(ALeft,ARight:TXalionRec):boolean; // 大于
    class operator GreaterThanOrEqual(ALeft,ARight:TXalionRec):boolean;  //大于等于
    class operator LessThan(ALeft,ARight:TXalionRec):boolean; // 小于
    class operator LessThanOrEqual(ALeft,ARight:TXalionRec):boolean; //小于等于
    class operator Inc(AValue:TXalionRec):TXalionRec;    // 递增
    class operator Dec(AValue:TXalionRec):TXalionRec;     // 递减

    class operator Add(AValue1:TXalionRec; AValue2:integer):TXalionRec;    // 加整数
    class operator Add(AValue1:TXalionRec; AValue2:TDateTime):TXalionRec;    //加时间
    class operator Add(AValue1:TXalionRec; AValue2:TXalionRec):TXalionRec;    // 直接加


    class operator Implicit(AValue:TDateTime):TXalionRec;  //显式等于日期
    class operator Implicit(AValue:integer):TXalionRec;    //显式等于整数

    class operator Implicit(AValue:TXalionRec):TDateTime; //显式赋值日期
    class operator Implicit(AValue:TXalionRec):integer; //显式赋值整数
end;


var
  Form2: TForm2;

implementation

{$R *.dfm}

{ TXalionRec }

class operator TXalionRec.Assign(var Dest:TXalionRec;const Src:TXalionRec);
 begin
     dest.ival:=src.ival;
     dest.dval:=src.dval;
 end;

class operator TXalionRec.Add(AValue1: TXalionRec;
  AValue2: TDateTime): TXalionRec;
begin
result:=  AValue1;
result.dval:=result.dval+avalue2;
end;

class operator TXalionRec.Add(AValue1: TXalionRec;
  AValue2: integer): TXalionRec;
begin
    result:=  AValue1;
     result.ival:=result.ival+avalue2;
end;

class operator TXalionRec.Add(AValue1:TXalionRec; AValue2:TXalionRec):TXalionRec;
begin
        result.ival :=avalue1.ival+avalue2.ival;
        result.dval:= avalue1.dval+avalue2.dval;
end;

constructor TXalionRec.create;
begin
    ival:=0;
    dval:=now;
end;

class operator TXalionRec.Dec(AValue: TXalionRec): TXalionRec;
begin
   result:=Avalue;
    dec(result.ival);
end;

destructor TXalionRec.Destroy;
begin
    exit;
end;

class operator TXalionRec.Equal(ALeft, ARight: TXalionRec): boolean;
begin
  result:=False;
    if Aleft.ival=Aright.ival then
    begin
        result:=True;
    end;

end;

class operator TXalionRec.GreaterThan(ALeft, ARight: TXalionRec): boolean;
begin
      result:=False;
       if Aleft.ival>Aright.ival then
          result:=True;
end;

class operator TXalionRec.GreaterThanOrEqual(ALeft,
  ARight: TXalionRec): boolean;
begin
    result:=False;
       if Aleft.ival>=Aright.ival then
          result:=True;
end;

class operator TXalionRec.Implicit(AValue: integer): TXalionRec;
begin
     result.ival:=Avalue;
end;

class operator TXalionRec.Implicit(AValue: TDateTime): TXalionRec;
begin
     result.dval:=Avalue;
end;

class operator TXalionRec.Implicit(AValue: TXalionRec): integer;
begin
    result:=Avalue.ival;
end;

class operator TXalionRec.Implicit(AValue: TXalionRec): TDateTime;
begin
      result:=Avalue.dval;
end;

class operator TXalionRec.Inc(AValue: TXalionRec): TXalionRec;
begin
    result:=Avalue;
    inc( result.ival);
end;

class operator TXalionRec.LessThan(ALeft, ARight: TXalionRec): boolean;
begin
      result:=False;
       if Aleft.ival<Aright.ival then
          result:=True;
end;

class operator TXalionRec.LessThanOrEqual(ALeft, ARight: TXalionRec): boolean;
begin
       result:=False;
       if Aleft.ival<=Aright.ival then
          result:=True;
end;

class operator TXalionRec.NotEqual(ALeft, ARight: TXalionRec): boolean;
begin
      result:=False;
       if Aleft.ival<>Aright.ival then
          result:=True;
end;



procedure TForm2.Button1Click(Sender: TObject);
var
   myrec,rec2:TXalionRec;
   d:Tdatetime;
begin

  myrec:=3;            //等于整数
   memo1.Lines.Add('myrec ival='+ myrec.ival.ToString);
  memo1.Lines.Add('myrec dval='+ formatdatetime('yyyy-mm-dd',myrec.dval));
  memo1.Lines.Add('>>>>>>>>>>>>>>>>>>end<<<<<<<<<<<<<<<<');


  inc(myrec);                 //递增
   memo1.Lines.Add('myrec ival='+ myrec.ival.ToString);
  memo1.Lines.Add('myrec dval='+ formatdatetime('yyyy-mm-dd',myrec.dval));
  memo1.Lines.Add('>>>>>>>>>>>>>>>>>>end<<<<<<<<<<<<<<<<');

  d:=2;
  myrec:=myrec+ d;                //加时间  2天
   memo1.Lines.Add('myrec ival='+ myrec.ival.ToString);
  memo1.Lines.Add('myrec dval='+ formatdatetime('yyyy-mm-dd',myrec.dval));
  memo1.Lines.Add('>>>>>>>>>>>>>>>>>>end<<<<<<<<<<<<<<<<');


  myrec:=myrec+5;       //加整数

  memo1.Lines.Add('myrec ival='+ myrec.ival.ToString);
  memo1.Lines.Add('myrec dval='+ formatdatetime('yyyy-mm-dd',myrec.dval));
  memo1.Lines.Add('>>>>>>>>>>>>>>>>>>end<<<<<<<<<<<<<<<<');

  rec2:=6;

  myrec:=myrec+rec2;


 memo1.Lines.Add('myrec ival='+ myrec.ival.ToString);
  memo1.Lines.Add('myrec dval='+ formatdatetime('yyyy-mm-dd',myrec.dval));
  memo1.Lines.Add('>>>>>>>>>>>>>>>>>>end<<<<<<<<<<<<<<<<');


end;

运行结果如图

可以看见非常灵活的实现各种操作，非常方便。