本教程演示用戶定義的類如何重載運算符。
請參見“運算符重載”示例以下載和生成本教程中討論的示例文件。
教程
運算符重載允許為運算指定用戶定義的運算符實現，其中一個或兩個操作數是用戶定義的類或結構類型。本教程包含兩個示例。第一個示例展示如何使用運算符重載創建定義復數加法的復數類。第二個示例展示如何使用運算符重載實現三值的邏輯類型。
本示例展示如何使用運算符重載創建定義復數加法的復數類 Complex。本程序使用 ToString 方法的重載顯示數字的虛部和實部以及加法結果。
// complex.cs
using System;
public struct Complex
{
public int real;
public int imaginary;
public Complex(int real, int imaginary)
{
this.real = real;
this.imaginary = imaginary;
}
// Declare which operator to overload (+), the types
// that can be added (two Complex objects), and the
// return type (Complex):
public static Complex operator +(Complex c1, Complex c2)
{
return new Complex(c1.real + c2.real, c1.imaginary + c2.imaginary);
}
// Override the ToString method to display an complex number in the suitable format:
public override string ToString()
{
return(String.Format("{0} + {1}i", real, imaginary));
}
public static void Main()
{
Complex num1 = new Complex(2,3);
Complex num2 = new Complex(3,4);
// Add two Complex objects (num1 and num2) through the
// overloaded plus operator:
Complex sum = num1 + num2;
// Print the numbers and the sum using the overriden ToString method:
Console.WriteLine("First complex number: {0}",num1);
Console.WriteLine("Second complex number: {0}",num2);
Console.WriteLine("The sum of the two numbers: {0}",sum);
}
}
First complex number: 2 + 3i Second complex number: 3 + 4i The sum of the two numbers: 5 + 7i
本示例展示如何使用運算符重載實現三值的邏輯類型。該類型的可能值有 DBBool.dbTrue、DBBool.dbFalse 和 DBBool.dbNull，其中 dbNull 成員表示未知值。
注意 定義 True 和 False 運算符只對表示 True、False 和 Null（既非 True 也非 False）的類型有用，如數據庫中使用的類型。
// dbbool.cs
using System;
public struct DBBool
{
// The three possible DBBool values:
public static readonly DBBool dbNull = new DBBool(0);
public static readonly DBBool dbFalse = new DBBool(-1);
public static readonly DBBool dbTrue = new DBBool(1);
// Private field that stores -1, 0, 1 for dbFalse, dbNull, dbTrue:
int value;
// Private constructor. The value parameter must be -1, 0, or 1:
DBBool(int value)
{
this.value = value;
}
// Implicit conversion from bool to DBBool. Maps true to
// DBBool.dbTrue and false to DBBool.dbFalse:
public static implicit operator DBBool(bool x)
{
return x? dbTrue: dbFalse;
}
// Explicit conversion from DBBool to bool. Throws an
// exception if the given DBBool is dbNull, otherwise returns
// true or false:
public static explicit operator bool(DBBool x)
{
if (x.value == 0) throw new InvalidOperationException();
return x.value > 0;
}
// Equality operator. Returns dbNull if either operand is dbNull,
// otherwise returns dbTrue or dbFalse:
public static DBBool operator ==(DBBool x, DBBool y)
{
if (x.value == 0 || y.value == 0) return dbNull;
return x.value == y.value? dbTrue: dbFalse;
}
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// Inequality operator. Returns dbNull if either operand is
// dbNull, otherwise returns dbTrue or dbFalse:
public static DBBool operator !=(DBBool x, DBBool y)
{
if (x.value == 0 || y.value == 0) return dbNull;
return x.value != y.value? dbTrue: dbFalse;
}
// Logical negation operator. Returns dbTrue if the operand is
// dbFalse, dbNull if the operand is dbNull, or dbFalse if the
// operand is dbTrue:
public static DBBool operator !(DBBool x)
{
return new DBBool(-x.value);
}
// Logical AND operator. Returns dbFalse if either operand is
// dbFalse, dbNull if either operand is dbNull, otherwise dbTrue:
public static DBBool operator &(DBBool x, DBBool y)
{
return new DBBool(x.value < y.value? x.value: y.value);
}
// Logical OR operator. Returns dbTrue if either operand is
// dbTrue, dbNull if either operand is dbNull, otherwise dbFalse:
public static DBBool operator |(DBBool x, DBBool y)
{
return new DBBool(x.value > y.value? x.value: y.value);
}
// Definitely true operator. Returns true if the operand is
// dbTrue, false otherwise:
public static bool operator true(DBBool x)
{
return x.value > 0;
}
// Definitely false operator. Returns true if the operand is
// dbFalse, false otherwise:
public static bool operator false(DBBool x)
{
return x.value < 0;
}
// Overload the conversion from DBBool to string:
public static implicit operator string(DBBool x)
{
return x.value > 0 ? "dbTrue"
: x.value < 0 ? "dbFalse"
: "dbNull";
}
// Override the Object.Equals(object o) method:
public override bool Equals(object o)
{
try
{
return (bool) (this == (DBBool) o);
}
catch
{
return false;
}
}
// Override the Object.GetHashCode() method:
public override int GetHashCode()
{
return value;
}
// Override the ToString method to convert DBBool to a string:
public override string ToString()
{
switch (value)
{
case -1:
return "DBBool.False";
case 0:
return "DBBool.Null";
case 1:
return "DBBool.True";
default:
throw new InvalidOperationException();
}
}
}
class Test
{
static void Main()
{
DBBool a, b;
a = DBBool.dbTrue;
b = DBBool.dbNull;
Console.WriteLine( "!{0} = {1}", a, !a);
Console.WriteLine( "!{0} = {1}", b, !b);
Console.WriteLine( "{0} & {1} = {2}", a, b, a & b);
Console.WriteLine( "{0} | {1} = {2}", a, b, a | b);
// Invoke the true operator to determine the Boolean
// value of the DBBool variable:
if (b)
Console.WriteLine("b is definitely true");
else
Console.WriteLine("b is not definitely true");
}
}
!DBBool.True = DBBool.False !DBBool.Null = DBBool.Null DBBool.True & DBBool.Null = DBBool.Null DBBool.True | DBBool.Null = DBBool.True b is not definitely true
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