其实 Delphi 2006 就已经支持运算符重载了, 不过 for Win32 的版本只是在 record 里支持.

运算符重载有什么用处呢? 举个例子:
譬如 "张三"、"李四" 两人一起来拜见你, 你可能会问: "你们两个谁大?"
其实你是在问: "你们两个谁的年龄大?"; 但生活中人们一般都不这么罗嗦.

在程序中能否这样简化呢? 这只能通过 "运算符重载" 做到!

先按 "你们两个谁的年龄大?" 写出原始例子吧:
--------------------------------------------------------------------------------

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

type
TMyRec = record
name: string;
age: Word;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
r1,r2: TMyRec;
str: string;
begin
r1.name := '张三'; r1.age := 18;
r2.name := '李四'; r2.age := 81;

if r1.age > r2.age then
str := r1.name
else
str := r2.name;

ShowMessageFmt('%s年龄大', [str]); {李四年龄大}
end;

end.
--------------------------------------------------------------------------------

上面是用 r1.age > r2.age 对比年龄, 如果能用 r1 > r2 来对比的话, 那就相当于: "你们两个谁大?" 了.

这样我们需要重载运算符 ">" ; 所谓重载运算符就是赋予某个运算符新的含义、新的功能.
我们可以重载的运算符只能是 Delphi 已有的运算符(还不是全部); C++ 也是这样.
需要用对应的指示字来表示这个运算符, 譬如: ">" 要用 GreaterThan 表示; C++ 不是这样.
重载运算符是通过方法实现的, 不过方法的指示字是 class operator (而非 function 或 proceture).

譬如上面的 record 可以这样声明:

type
TMyRec = record
name: string;
age: Word;
class operator GreaterThan(a,b: TMyRec): Boolean;
end;

还得有方法的实现(遗憾的是有些不能用 Ctrl+Shift+C 自动建立, 那就复制吧):

class operator TMyRec.GreaterThan(a,b: TMyRec): Boolean; {注意复制后再加上方法名: "TMyRec."}
begin
Result := a.age > b.age;
end;

下面是完整的代码:
--------------------------------------------------------------------------------

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

type
TMyRec = record
name: string;
age: Word;
class operator GreaterThan(a,b: TMyRec): Boolean;
end;

class operator TMyRec.GreaterThan(a,b: TMyRec): Boolean;
begin
Result := a.age > b.age;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
r1,r2: TMyRec;
str: string;
begin
r1.name := '张三'; r1.age := 18;
r2.name := '李四'; r2.age := 81;

if r1 > r2 then
str := r1.name
else
str := r2.name;

ShowMessageFmt('%s年龄大', [str]); {李四年龄大}
end;

end.
--------------------------------------------------------------------------------

这个测试里面有一些漏洞, 譬如: 年龄相等怎么办? 不必较真, 只是借此说明一个道理而已.

可重载运算符列表

类别	运算符	运算符标识	使用
转换	隐式转换	Implicit	Implicit(a: type): resultType;
	显式转换	Explicit	Explicit(a: type): resultType;
一元	-	Negative	Negative(a: type): resultType;
	+	Positive	Positive(a: type): resultType;
	Inc	Inc	Inc(a: type): resultType;
	Dec	Dec	Dec(a: type): resultType
	not	LogicalNot	LogicalNot(a: type): resultType;
	not	BitwiseNot	BitwiseNot(a: type): resultType;
	Trunc	Trunc	Trunc(a: type): resultType;
	Round	Round	Round(a: type): resultType;
比较	=	Equal	Equal(a: type; b: type): Boolean;
	<>	NotEqual	NotEqual(a: type; b: type): Boolean;
	>	GreaterThan	GreaterThan(a: type; b: type) Boolean;
	>=	GreaterThanOrEqual	GreaterThanOrEqual(a: type; b: type): resultType;
	<	LessThan	LessThan(a: type; b: type): resultType;
	<=	LessThanOrEqual	LessThanOrEqual(a: type; b: type): resultType;
二元	+	Add	Add(a: type; b: type): resultType;
	-	Subtract	Subtract(a: type; b: type): resultType;
	*	Multiply	Multiply(a: type; b: type): resultType;
	/	Divide	Divide(a: type; b: type): resultType;
	div	IntDivide	IntDivide(a: type; b: type): resultType;
	mod	Modulus	Modulus(a: type; b: type): resultType;
	shl	LeftShift	LeftShift(a: type; b: type): resultType;
	shr	RightShift	RightShift(a: type; b: type): resultType;
	and	LogicalAnd	LogicalAnd(a: type; b: type): resultType;
	or	LogicalOr	LogicalOr(a: type; b: type): resultType;
	xor	LogicalXor	LogicalXor(a: type; b: type): resultType;
	and	BitwiseAnd	BitwiseAnd(a: type; b: type): resultType;
	or	BitwiseOr	BitwiseOr(a: type; b: type): resultType;
	xor	BitwiseXor	BitwiseXor(a: type; b: type): resultType;