自定义包容性TakeWhile()，还有更好的方法吗? [英] Custom Inclusive TakeWhile(), is there a better way?

问题描述

我编写了一个自定义LINQ扩展方法，该方法将TakeWhile()方法扩展为包含的，而不是在谓词为false时将其扩展.

I've written a custom LINQ extension method that extends the TakeWhile() method to be inclusive, rather than exclusive when the predicate is false.

        public static IEnumerable<T> TakeWhile<T>(this IEnumerable<T> source, Func<T, bool> predicate, bool inclusive)
        {
            source.ThrowIfNull("source");
            predicate.ThrowIfNull("predicate");

            if (!inclusive)
                return source.TakeWhile(predicate);

            var totalCount = source.Count();
            var count = source.TakeWhile(predicate).Count();

            if (count == totalCount)
                return source;
            else
                return source.Take(count + 1);
        }

虽然可行，但我确信有更好的方法.我相当确定，就延迟执行/加载而言，这是行不通的.

While this works, I'm sure there is a better way of doing it. I'm fairly sure that this doesn't work in terms of deferred execution/loading.

ThrowIfNull()是用于ArgumentNullException检查的扩展方法

ThrowIfNull() is a extension method for ArgumentNullException checking

社区可以提供一些提示或重写吗? :)

Can the community provide some some hints or re-writes? :)

推荐答案

您是对的；这对推迟执行不友好(调用Count需要对源进行完整枚举).

You are correct; this is not friendly to deferred execution (calling Count requires a full enumeration of the source).

但是，您可以这样做:

public static IEnumerable<T> TakeWhile<T>(this IEnumerable<T> source, Func<T, bool> predicate, bool inclusive)
{
    foreach(T item in source)
    {
        if(predicate(item)) 
        {
            yield return item;
        }
        else
        {
            if(inclusive) yield return item;

            yield break;
        }
    }
} 

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