c# MoreLinq 之 Acquire

前言

本系列是对MoreLinq库的学习与总结，分析各个Api的实现方式及用法，也为能写出更高效的Linq打下基础。

1. Acquire 确保，保证

void AcquireTest()
{
    Disposable a = null!;
    Disposable b = null!;
    Disposable c = null!;
    var allocators = MoreEnumerable.From(() => a = new Disposable(),
    () => b = new Disposable(),
    () => throw new Exception(),
    () => c = new Disposable()
    );
    allocators.Acquire();
}
class Disposable : IDisposable
{
    public bool Disposed { get; private set; }
    public void Dispose() { Disposed = true; }
}

static partial class MoreEnumerable
{

    /// <summary>
    /// Ensures that a source sequence of <see cref="IDisposable"/>
    /// objects are all acquired successfully. If the acquisition of any
    /// one <see cref="IDisposable"/> fails then those successfully
    /// acquired till that point are disposed.
    /// </summary>
    /// <typeparam name="TSource">Type of elements in <paramref name="source"/> sequence.</typeparam>
    /// <param name="source">Source sequence of <see cref="IDisposable"/> objects.</param>
    /// <returns>
    /// Returns an array of all the acquired <see cref="IDisposable"/>
    /// objects in source order.
    /// </returns>
    /// <remarks>
    /// This operator executes immediately.
    /// </remarks>
    //Acquire 顺序执行,如果失败则顺序释放资源
    public static TSource[] Acquire<TSource>(this IEnumerable<TSource> source) where TSource : IDisposable
    {
        if (source == null) throw new ArgumentNullException(nameof(source));
        var disposables = new List<TSource>();
        try
        {
            disposables.AddRange(source);
            return disposables.ToArray();//到此开始执行
        }
        catch
        {
            foreach (var disposable in disposables)
            {
                disposable.Dispose();//释放资源
            }
            throw;
        }
    }

    //Evaluate
    public static IEnumerable<T> Evaluate<T>(this IEnumerable<Func<T>> functions) =>
      from f in functions ?? throw new ArgumentNullException(nameof(functions))
      select f();

    //From
    public static IEnumerable<T> From<T>(params Func<T>[] functions)
    {
        if (functions == null) throw new ArgumentNullException(nameof(functions));
        return Evaluate(functions);
    }
}

这个方法主要实现的是：当Enumerable中有需要释放资源的对象时且有可能抛异常，使用这个方法之后能保证已经打开的对象能正确关闭。
在这个测试用例里使用了From方法，From方法实现动态调用执行，及调用了Evaluate方法，如下：

    //Evaluate
    public static IEnumerable<T> Evaluate<T>(this IEnumerable<Func<T>> functions) =>
      from f in functions ?? throw new ArgumentNullException(nameof(functions))
      select f();

本文作者：wwmin
微信公众号: DotNet技术说
本文链接：https://www.jianshu.com/p/32855aa37e12
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