== VS等于C＃ [英] == vs Equals in C#

问题描述

是什么==评价之间的差异，在C＃等于？

有关防爆，

 如果（X == X ++）//始终返回true，
  

但

 如果（x.Equals（X ++））//始终返回false 
  

编辑：

  INT X = 0; 
 INT Y = 0; 
 
如果（x.Equals（Y ++））//返回True 
  

解决方案

根据规范，这是预期的行为。

第一次的行为是规范的7.3节管辖。

<在表达式块引用>

操作数从左至右进行评价。例如，在 F（I）+ G（我+ +）* H（I），方法F使用我的旧值被调用，那么方法G称为与我的旧值，并且，最后，方法H称为与i的新值。在这是独立且无运算符优先级。






因此​​Y == X ++ ，第一左操作数进行评估（ 0 ），然后右手被评估（ 0 ， X 变成 1 ），则比较完成： 0 == 0 是真的

第二的行为是由部分7.5.5决定：

• 如果M是在的值类型中声明的实例函数成员的：
  
  
  
  • E是评估。如果此计算导致异常，则不执行进一步的操作。
  
  
  • 如果E没有被归类为一个变量，那么E同类型的临时局部变量被创建和E的值分配给该变量。则E被重新归类为对该临时局部变量的引用。临时变量是如此访问内男，但不以任何其他方式。因此，只有当E是一个真正的变量是有可能调用者观察到M对this所做的更改。
  
  
  • 参数清单中的第7.5.1节所述进行评价。
  
  
  • M被调用。 E引用的变量成为this引用的变量。
  
  

注意值类型参照以自己的方式通过。

因此，在 X。等于（X ++），第一个目标是评估（E是 X ，一个变量），那么参数计算（ 0 ， X 变成 1 ），则比较完成：<$ C 。$ C> x.Equals（0）为假

编辑：我也想给信贷DTB现在缩回评论，张贴而这个问题被关闭。我想他是在说同样的事情，但对注释的长度限制他不能够完全表达出来。

What is the difference between the evaluation of == and Equals in C#?

For Ex,

if(x==x++)//Always returns true

but

if(x.Equals(x++))//Always returns false 

Edited:

     int x=0;
     int y=0;

     if(x.Equals(y++))// Returns True

解决方案

According to the specification, this is expected behavior.

The behavior of the first is governed by section 7.3 of the spec:

Operands in an expression are evaluated from left to right. For example, in F(i) + G(i++) * H(i), method F is called using the old value of i, then method G is called with the old value of i, and, finally, method H is called with the new value of i. This is separate from and unrelated to operator precedence.

Thus in x==x++, first the left operand is evaluated (0), then the right-hand is evaluated (0, x becomes 1), then the comparison is done: 0 == 0 is true.

The behavior of the second is governed by section 7.5.5:

• If M is an instance function member declared in a value-type:
  • E is evaluated. If this evaluation causes an exception, then no further steps are executed.
  • If E is not classified as a variable, then a temporary local variable of E’s type is created and the value of E is assigned to that variable. E is then reclassified as a reference to that temporary local variable. The temporary variable is accessible as this within M, but not in any other way. Thus, only when E is a true variable is it possible for the caller to observe the changes that M makes to this.
  • The argument list is evaluated as described in §7.5.1.
  • M is invoked. The variable referenced by E becomes the variable referenced by this.

Note that value types are passed by reference to their own methods.

Thus in x.Equals(x++), first the target is evaluated (E is x, a variable), then the arguments are evaluated (0, x becomes 1), then the comparison is done: x.Equals(0) is false.

EDIT: I also wanted to give credit to dtb's now-retracted comment, posted while the question was closed. I think he was saying the same thing, but with the length limitation on comments he wasn't able to express it fully.

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