如何使用Lambda表达式创建扩展方法 [英] How to create extension methods with lambda expressions

问题描述

当前，我正在创建一个接受参数的扩展方法.使用以下示例，如何使用lambda表达式进行转换?

Currently i am creating an extension method that accepts parameters. Using the below example, how could one convert this using lambda expressions?

public static decimal ChangePercentage(this IEnumerable<Trade> trades, DateTime startDate, DateTime endDate)
{
    var query = from trade in trades
                where trade.TradeTime >= startDate
                where trade.TradeTime <= endDate
                orderby trade.TradeTime descending
                select trade;
    return (query.First().Value - query.Last().Value) / query.First().Value * 100;
}

使用lambda与常规方法参数相比，优点/缺点是什么?

What are the pro/cons using lambda vs normal method parameters?

谢谢

推荐答案

可以将示例更改为使用lambda表达式的一种方法是使用过滤器.

One way you could change the sample to use lambda expressions is to use a filter.

public static decimal ChangePercentage(this IEnumerable<Trade> trades, 
                                       Func<Trade,bool> pred)
        {
            var query = from trade in trades
                        where pred(trade);
                        orderby trade.TradeTime descending
                        select trade;
            return (query.First().Value - query.Last().Value) / query.First().Value * 100;
        }

    someTrades.ChangePercentage(x => x.TradeDate >= startDate && x.TradeTime <= endDate);

这给您带来的最大好处就是灵活性.而不是使用基于日期的过滤进行计算的方法.您有一种方法，可以使用灵活的过滤器方法来计算百分比.

The biggest pro this gives you is flexbility. Instead of having a method which does date based filtering for calculation. You have a method with a flexible filter method for calculating percentages.

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