T＆GT;＆懒LT的执行情况;对于.NET 3.5 [英] Implementation of Lazy<T> for .NET 3.5

问题描述

.NET 4.0有一个名为 System.Lazy 一个很好的工具类，做懒对象初始化。我想使用这个类为3.5的项目。有一次我看到某处的实施在计算器的答案，但我无法找到它了。是否有人有另一种实现懒惰的？它并不需要所有的框架4.0版本的线程安全功能。

.NET 4.0 has a nice utility class called System.Lazy that does lazy object initialization. I would like to use this class for a 3.5 project. One time I saw an implementation somewhere in a stackoverflow answer but I can't find it anymore. Does someone have an alternative implementation of Lazy? It doesn't need all the thread safety features of the framework 4.0 version.

更新：

解答包含非线程安全的，一个线程安全的版本。

Answers contain a non thread safe and a thread safe version.

推荐答案

下面是我使用的实现。

/// <summary>
/// Provides support for lazy initialization.
/// </summary>
/// <typeparam name="T">Specifies the type of object that is being lazily initialized.</typeparam>
public sealed class Lazy<T>
{
    private readonly object padlock = new object();
    private readonly Func<T> createValue;
    private bool isValueCreated;
    private T value;

    /// <summary>
    /// Gets the lazily initialized value of the current Lazy{T} instance.
    /// </summary>
    public T Value
    {
        get
        {
            if (!isValueCreated)
            {
                lock (padlock)
                {
                    if (!isValueCreated)
                    {
                        value = createValue();
                        isValueCreated = true;
                    }
                }
            }
            return value;
        }
    }

    /// <summary>
    /// Gets a value that indicates whether a value has been created for this Lazy{T} instance.
    /// </summary>
    public bool IsValueCreated
    {
        get
        {
            lock (padlock)
            {
                return isValueCreated;
            }
        }
    }


    /// <summary>
    /// Initializes a new instance of the Lazy{T} class.
    /// </summary>
    /// <param name="createValue">The delegate that produces the value when it is needed.</param>
    public Lazy(Func<T> createValue)
    {
        if (createValue == null) throw new ArgumentNullException("createValue");

        this.createValue = createValue;
    }


    /// <summary>
    /// Creates and returns a string representation of the Lazy{T}.Value.
    /// </summary>
    /// <returns>The string representation of the Lazy{T}.Value property.</returns>
    public override string ToString()
    {
        return Value.ToString();
    }
}

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