性能：始终分配布尔值或先检查值？ [英] Performance: assign boolean value always or check value first?

问题描述

我敢肯定，这是微不足道的，但因为我想从一个方法中指定真来一个布尔字段，这是否选择有什么区别？如果是这样，为什么？

 字段= TRUE; //可能已经是事实，但我不在乎
 

与

 如果字段= TRUE（场！）;
 

解决方案

我会说不。但是，这不依赖于一个事实，即我们真的在谈论的字段的，而不是一个的属性的，它的可以（虽然它绝对不应该）表现出不同的行为在你包括两个片段（即，如果没有与在吸气剂的副作用）的逻辑。

更新：如果你在谈论的性能开销，几乎没有任何difference- 但是我相信任务是不断所谓价格稍微低一些（比读值）。下面是一个示例程序来证明这一点：

 布尔B = FALSE;

秒表SW = Stopwatch.StartNew（）;
的for（int i = 0; I＆LT; int.MaxValue ++ I）
{
    B =真实;
}
sw.Stop（）;

时间跨度setNoCheckTime = sw.Elapsed;

SW = Stopwatch.StartNew（）;
的for（int i = 0; I＆LT; int.MaxValue ++ I）
{
    //这部分将不会指派，为b将永远是正确的。
    如果（！B）
    {
        B =真实;
    }
}
sw.Stop（）;

时间跨度checkSetTime = sw.Elapsed;

Console.WriteLine（分配：{0}毫秒，setNoCheckTime.TotalMilliseconds）;
Console.WriteLine（读：{0}毫秒，checkSetTime.TotalMilliseconds）;
 

输出我的机器上：

分配：2749.6285毫秒
阅读：4543.0343毫秒

I'm sure it is negligible, but given that I want to assign true to a boolean field from within a method, does this choice make any difference? If so, why?

field = true; // could already be true, but I don't care

versus

if(!field) field = true;

解决方案

I'd say no. But this does depend on the fact that we really are talking about a field as opposed to a property, which may (though it definitely should not) exhibit different behavior in the two snippets you included (i.e., if there is logic with side effects in the getter).

Update: If you're talking about performance overhead, there is practically no difference—but I believe assignment is ever-so-slightly less expensive (than reading the value). Here is a sample program to demonstrate this:

bool b = false;

Stopwatch sw = Stopwatch.StartNew();
for (int i = 0; i < int.MaxValue; ++i)
{
    b = true;
}
sw.Stop();

TimeSpan setNoCheckTime = sw.Elapsed;

sw = Stopwatch.StartNew();
for (int i = 0; i < int.MaxValue; ++i)
{
    // This part will never assign, as b will always be true.
    if (!b)
    {
        b = true;
    }
}
sw.Stop();

TimeSpan checkSetTime = sw.Elapsed;

Console.WriteLine("Assignment: {0} ms", setNoCheckTime.TotalMilliseconds);
Console.WriteLine("Read: {0} ms", checkSetTime.TotalMilliseconds);

Output on my machine:

Assignment: 2749.6285 ms
Read: 4543.0343 ms

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