请告诉我最有效的方式来实例化工人变量

例如我的工人变量

一个）

bool b = default(bool); 

for (int i = 0; i < MyCollection.Length; i++) 
{ 
    b = false; 

    foreach(object myObject in myObjectCollection) 
    { 
    if (object.Property == MyCollection[i].Property) 
    { 
     b = true; 
     break; 
    } 
    }  

    if (b) 
    { 
    DoSomethingWith(MyCollection[i]); 
    } 
}

B）

for (int i = 0; i < MyCollection.Length; i++) 
{ 
    bool b = default(bool); 

    foreach(object myObject in myObjectCollection) 
    { 
    if (object.Property == MyCollection[i].Property) 
    { 
     b = true; 
     break; 
    } 
    }  

    if (b) 
    { 
    DoSomethingWith(MyCollection[i]); 
    } 
}

编辑：好像普遍认为不会有差异，其中IL而言。但对于可读性和清晰度的范围内......不如

来源

2008-12-18 Nick Allen

我曾经在外面做过，但ReSharper告诉我要在里面做。我会对人们的回复感兴趣 – 2008-12-18 15:12:50

“bool b = default（bool）”非常古怪！ – mackenir 2008-12-18 15:30:06

以前的答案被删除，因为我会误读代码。（使用“默认（布尔）”的任何地方是有点奇怪，顺便说一句。）

然而，除非该变量由委托等拍摄，我期望他们要么编译成IL，其实际上是相同（就行为和性能而言）。

与以往一样，先写最可读代码。微这样的事情正在寻求麻烦。我同意那些建议你尽可能多地限制变量范围的人 - 所以如果你在循环之后需要它，反正你没有选择;否则在里面声明它。

好，这是一个测试程序：

using System; 

class Test 
{ 
    static void Main() {} 

    static void DeclareInside() 
    { 
     for (int i=0; i < 10; i++) 
     { 
      bool x = false; 
      for (int j=5; j < 20; j++) 
      { 
       if (i == j) 
       { 
        x = true; 
        break; 
       } 
       if (x) 
       { 
        Console.WriteLine("Yes"); 
       } 
      } 
     } 
    } 

    static void DeclareOutside() 
    { 
     bool x; 
     for (int i=0; i < 10; i++) 
     { 
      x = false; 
      for (int j=5; j < 20; j++) 
      { 
       if (i == j) 
       { 
        x = true; 
        break; 
       } 
       if (x) 
       { 
        Console.WriteLine("Yes"); 
       } 
      } 
     } 
    } 
}

产生IL（只是csc Test.cs）：

.method private hidebysig static void DeclareOutside() cil managed 
{ 
    // Code size  79 (0x4f) 
    .maxstack 2 
    .locals init (bool V_0, 
      int32 V_1, 
      int32 V_2, 
      bool V_3) 
    IL_0000: nop 
    IL_0001: ldc.i4.0 
    IL_0002: stloc.1 
    IL_0003: br.s  IL_0045 
    IL_0005: nop 
    IL_0006: ldc.i4.0 
    IL_0007: stloc.0 
    IL_0008: ldc.i4.5 
    IL_0009: stloc.2 
    IL_000a: br.s  IL_0037 
    IL_000c: nop 
    IL_000d: ldloc.1 
    IL_000e: ldloc.2 
    IL_000f: ceq 
    IL_0011: ldc.i4.0 
    IL_0012: ceq 
    IL_0014: stloc.3 
    IL_0015: ldloc.3 
    IL_0016: brtrue.s IL_001d 
    IL_0018: nop 
    IL_0019: ldc.i4.1 
    IL_001a: stloc.0 
    IL_001b: br.s  IL_0040 
    IL_001d: ldloc.0 
    IL_001e: ldc.i4.0 
    IL_001f: ceq 
    IL_0021: stloc.3 
    IL_0022: ldloc.3 
    IL_0023: brtrue.s IL_0032 
    IL_0025: nop 
    IL_0026: ldstr  "Yes" 
    IL_002b: call  void [mscorlib]System.Console::WriteLine(string) 
    IL_0030: nop 
    IL_0031: nop 
    IL_0032: nop 
    IL_0033: ldloc.2 
    IL_0034: ldc.i4.1 
    IL_0035: add 
    IL_0036: stloc.2 
    IL_0037: ldloc.2 
    IL_0038: ldc.i4.s 20 
    IL_003a: clt 
    IL_003c: stloc.3 
    IL_003d: ldloc.3 
    IL_003e: brtrue.s IL_000c 
    IL_0040: nop 
    IL_0041: ldloc.1 
    IL_0042: ldc.i4.1 
    IL_0043: add 
    IL_0044: stloc.1 
    IL_0045: ldloc.1 
    IL_0046: ldc.i4.s 10 
    IL_0048: clt 
    IL_004a: stloc.3 
    IL_004b: ldloc.3 
    IL_004c: brtrue.s IL_0005 
    IL_004e: ret 
} // end of method Test::DeclareOutside 

.method private hidebysig static void DeclareInside() cil managed 
{ 
    // Code size  79 (0x4f) 
    .maxstack 2 
    .locals init (int32 V_0, 
      bool V_1, 
      int32 V_2, 
      bool V_3) 
    IL_0000: nop 
    IL_0001: ldc.i4.0 
    IL_0002: stloc.0 
    IL_0003: br.s  IL_0045 
    IL_0005: nop 
    IL_0006: ldc.i4.0 
    IL_0007: stloc.1 
    IL_0008: ldc.i4.5 
    IL_0009: stloc.2 
    IL_000a: br.s  IL_0037 
    IL_000c: nop 
    IL_000d: ldloc.0 
    IL_000e: ldloc.2 
    IL_000f: ceq 
    IL_0011: ldc.i4.0 
    IL_0012: ceq 
    IL_0014: stloc.3 
    IL_0015: ldloc.3 
    IL_0016: brtrue.s IL_001d 
    IL_0018: nop 
    IL_0019: ldc.i4.1 
    IL_001a: stloc.1 
    IL_001b: br.s  IL_0040 
    IL_001d: ldloc.1 
    IL_001e: ldc.i4.0 
    IL_001f: ceq 
    IL_0021: stloc.3 
    IL_0022: ldloc.3 
    IL_0023: brtrue.s IL_0032 
    IL_0025: nop 
    IL_0026: ldstr  "Yes" 
    IL_002b: call  void [mscorlib]System.Console::WriteLine(string) 
    IL_0030: nop 
    IL_0031: nop 
    IL_0032: nop 
    IL_0033: ldloc.2 
    IL_0034: ldc.i4.1 
    IL_0035: add 
    IL_0036: stloc.2 
    IL_0037: ldloc.2 
    IL_0038: ldc.i4.s 20 
    IL_003a: clt 
    IL_003c: stloc.3 
    IL_003d: ldloc.3 
    IL_003e: brtrue.s IL_000c 
    IL_0040: nop 
    IL_0041: ldloc.0 
    IL_0042: ldc.i4.1 
    IL_0043: add 
    IL_0044: stloc.0 
    IL_0045: ldloc.0 
    IL_0046: ldc.i4.s 10 
    IL_0048: clt 
    IL_004a: stloc.3 
    IL_004b: ldloc.3 
    IL_004c: brtrue.s IL_0005 
    IL_004e: ret 
} // end of method Test::DeclareInside

的唯一区别是其中的变量位于堆栈中。

来源

2008-12-18 15:16:39

我想声明它们的循环中，它节省了一行代码（声明，并将其设置在同一行），并且更容易看到什么我在循环范围之外使用的变量，当你在处理复杂的事情时这很好。

来源

2008-12-18 15:14:08

内部看起来比较清爽，但同意与Jon的IL将是相同的。

来源

2008-12-18 15:15:41

内。变量的范围应该根据实际使用情况而定。声明它在范围之外的变量包含块是不必要的，可能会导致混淆。

编辑：我猜测，这个代码只是为了说明的例子，但其实我省略了多余的变量，并把它写成：

for (int i = 0; i < MyCollection.Length; i++) 
{ 
    foreach(MyObjectClass myObject in myObjectCollection) 
    { 
     if (myObject.Property == MyCollection[i].Property) 
     { 
      DoSomethingWith(MyCollection[i]); 
      break; 
     } 
    } 
}

来源

2008-12-18 15:18:22 tvanfosson