运算符重载和LINQ总和在C＃

问题描述

我有一个自定义类型（理财），有一个隐式的转换为十进制和重载运算符 + 。当我有这种类型的列表，并调用LINQ 总和方法的结果是小数，而不是理财。我怎么可以给 + 操作符presidence和回款的总和？

 内部类测试
{
    void示例（）
    {
        VAR名单=新的[] {新钱（10，英镑），新钱（20，英镑）};
        //此行编译失败，因为没有隐
        //转换从十进制的钱
        金钱的结果= list.Sum（X =＆GT; X）;
    }
}


公共类理财
{
    私人货币_currency;
    私人字符串_iso3Letter code;

    公共小数？金额{获得;组; }
    公共外币货币
    {
        {返回_currency; }
        组
        {
            _iso3Letter code = value.Iso3Letter code;
            _currency =价值;
        }
    }

    公款（十进制？量，串iso3LetterCurrency code）
    {
        金额=金额;
        货币= Currency.FromIso3Letter code（iso3LetterCurrency code）;
    }

    公共静态钱运营商+（钱C1，C2的钱）
    {
        如果（c1.Currency！= c2.Currency）
            抛出新的ArgumentException（的String.Format（无法​​添加混合货币{0}不同于{1}，
                                                      c1.Currency，c2.Currency））;
        VAR值= c1.Amount + c2.Amount;
        返回新的货币（值，c1.Currency）;
    }

    公共静态隐含的运营商小数？（钱生钱）
    {
        返回money.Amount;
    }

    公共静态隐含运营十进制（钱生钱）
    {
        返回money.Amount？ 0;
    }
}
 

解决方案

总和只知道数类型系统。

您可以使用总结是这样的：

 理财结果= list.Aggregate（（X，Y）=＆GT; X + Y）;
 

由于这是调用总结＆LT;钱＆GT; ，它会使用你的 Money.operator + 并返回理财对象。

I have a custom type (Money) that has an implict conversion to decimal and an overloaded operator for +. When I have a list of these types and call the linq Sum method the result is decimal, not Money. How can I give the +operator presidence and return Money from the Sum?

internal class Test
{
    void Example()
    {
        var list = new[] { new Money(10, "GBP"), new Money(20, "GBP") };
        //this line fails to compile as there is not implicit 
        //conversion from decimal to money
        Money result = list.Sum(x => x);
    }
}


public class Money
{
    private Currency _currency;
    private string _iso3LetterCode;

    public decimal? Amount { get; set; }
    public Currency Currency
    {
        get {  return _currency; }
        set
        {
            _iso3LetterCode = value.Iso3LetterCode; 
            _currency = value; 
        }
    }

    public Money(decimal? amount, string iso3LetterCurrencyCode)
    {
        Amount = amount;
        Currency = Currency.FromIso3LetterCode(iso3LetterCurrencyCode);
    }

    public static Money operator +(Money c1, Money c2)
    {
        if (c1.Currency != c2.Currency)
            throw new ArgumentException(string.Format("Cannot add mixed currencies {0} differs from {1}",
                                                      c1.Currency, c2.Currency));
        var value = c1.Amount + c2.Amount;
        return new Money(value, c1.Currency);
    }

    public static implicit operator decimal?(Money money)
    {
        return money.Amount;
    }

    public static implicit operator decimal(Money money)
    {
        return money.Amount ?? 0;
    }
}

解决方案

Sum only knows about the number types in System.

You can use Aggregate like this:

Money result = list.Aggregate((x,y) => x + y);

Because this is calling Aggregate<Money>, it will use your Money.operator+ and return a Money object.

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