C# - 演算子のオーバーロード(等価演算子、Equalsメソッドのオーバーロード)

開発環境

• Microsoft Windows 7 Home Premium (OS)
• Microsoft Visual C# 2010 Express Edition (IDE)
• 言語: C#

『初めてのC# 第2版』(Jesse Liberty+Brian MacDonald著、日向俊二訳、オライリー・ジャパン、2006年、ISBN978-487311-294-7)の 第12章(演算子のオーバーロード)12.6(練習問題)、練習12-2を解いてみる。

練習12-2.

コード

using System;

namespace Sample
{
    public class Invoice
    {
        private string vendor;
        private double amount;
        public Invoice(string vendor, double amount)
        {
            this.vendor = vendor;
            this.amount = amount;
        }
        public static Invoice operator +(Invoice lhs, Invoice rhs)
        {
            if (lhs.vendor == rhs.vendor)
            {
                return new Invoice(lhs.vendor, lhs.amount + rhs.amount);
            }
            return new Invoice("", 0);
        }
        public static bool operator ==(Invoice lhs, Invoice rhs)
        {
            if (lhs.vendor == rhs.vendor && lhs.amount == rhs.amount)
            {
                return true;
            }
            return false;
        }
        public static bool operator !=(Invoice lhs, Invoice rhs)
        {
            return !(lhs == rhs);
        }
        public override bool Equals(object obj)
        {
            if (!(obj is Invoice))
            {
                return false;
            }
            return this == (Invoice)obj;
        }
        public string Vendor
        {
            get { return vendor; }
        }
        public double Amount
        {
            get { return amount; }
        }
    }
    class Tester
    {
        public void Run()
        {
            Invoice a = new Invoice("invoice1", 10);
            Invoice b = new Invoice("invoice1", 10);
            Invoice c = new Invoice("invoice1", 20);
            Invoice d = new Invoice("invoice2", 10);
            Invoice e = new Invoice("invoice2", 20);
            Invoice[] invoices = { b, c, d, e };
            foreach (Invoice invoice in invoices)
            {
                Console.WriteLine("({0},{1}) == ({2},{3}): {4}",
                   a.Vendor, a.Amount, invoice.Vendor, invoice.Amount,
                   a == invoice);
            }
        }
        static void Main()
        {
            Tester t = new Tester();
            t.Run();
        }
    }
}

入出力結果(Console Window)

(invoice1,10) == (invoice1,10): True
(invoice1,10) == (invoice1,20): False
(invoice1,10) == (invoice2,10): False
(invoice1,10) == (invoice2,20): False
続行するには何かキーを押してください . . .