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ConditionalAttribute是应该去掉整行,还是仅仅是方法调用?

release conditional debugging .net

Dan Tao · 技术社区 · 14 年前

ConditionalAttribute 班级:

将条件属性应用于方法向编译器指示对方法的调用不应为编译为Microsoft中级语言(MSIL),除非关联的编译符号已定义with conditional属性。

对我来说这意味着 Conditional

class InstanceType
{
    public InstanceType DoSideEffects()
    {
        Console.WriteLine("Side effects!");
        return this;
    }

    public InstanceType DoMoreSideEffects()
    {
        Console.WriteLine("More side effects!");
        return this;
    }

    [Conditional("DEBUG")]
    public void ConditionalMethod()
    {
        Console.WriteLine("Conditional method run.");
    }
}

class Program
{
    static void Main()
    {
        var x = new InstanceType();

        // The compiler appears to strip out this entire line
        // in a Release build.
        x.DoSideEffects().DoMoreSideEffects().ConditionalMethod();

        var y = new InstanceType();

        // When each method call appears on its own line,
        // the first two methods are included as expected.
        y.DoSideEffects();
        y.DoMoreSideEffects();
        y.ConditionalMethod();
    }
}

比较调试和发布版本的输出:

DEBUG                    RELEASE
Side effects!            Side effects!
More side effects!       More side effects!
Conditional method run.
Side effects!
More side effects!
Conditional method run.

这种行为是在什么地方规定的吗? 我以为这两个构建都应该有相同的输出,除了读取“Conditional method run”的行

2 回复 | 直到 14 年前

Maate 14 年前

有趣的特点:我从来没注意到。

整个C#代码行在IL中明显被忽略了:

在调试编译中创建(x变量),存储三种方法都适用依次为:DoSideEffects(), 条件方法()
在版本编译中,仍然会创建该变量,但由于不需要它,它会立即弹出。相反,y变量存储在位置0并加载。

对我来说,这看起来像只虫子,真的。似乎可以在IL中排除ConditionalMethod()调用。但似乎你是对的,整条线都被遗漏了。

// DEBUG compilation
.method private hidebysig static void  Main() cil managed
{
  .entrypoint
  // Code size       58 (0x3a)
  .maxstack  1
  .locals init (class ConsoleApplication3.InstanceType V_0,
           class ConsoleApplication3.InstanceType V_1)
  IL_0000:  nop
  IL_0001:  newobj     instance void ConsoleApplication3.InstanceType::.ctor()
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  callvirt   instance class ConsoleApplication3.InstanceType ConsoleApplication3.InstanceType::DoSideEffects()
  IL_000d:  callvirt   instance class ConsoleApplication3.InstanceType ConsoleApplication3.InstanceType::DoMoreSideEffects()
  IL_0012:  callvirt   instance void ConsoleApplication3.InstanceType::ConditionalMethod()
  IL_0017:  nop
  IL_0018:  newobj     instance void ConsoleApplication3.InstanceType::.ctor()
  IL_001d:  stloc.1
  IL_001e:  ldloc.1
  IL_001f:  callvirt   instance class ConsoleApplication3.InstanceType ConsoleApplication3.InstanceType::DoSideEffects()
  IL_0024:  pop
  IL_0025:  ldloc.1
  IL_0026:  callvirt   instance class ConsoleApplication3.InstanceType ConsoleApplication3.InstanceType::DoMoreSideEffects()
  IL_002b:  pop
  IL_002c:  ldloc.1
  IL_002d:  callvirt   instance void ConsoleApplication3.InstanceType::ConditionalMethod()
  IL_0032:  nop
  IL_0033:  call       valuetype [mscorlib]System.ConsoleKeyInfo [mscorlib]System.Console::ReadKey()
  IL_0038:  pop
  IL_0039:  ret
} // end of method Program::Main

// RELEASE compilation
.method private hidebysig static void  Main() cil managed
{
  .entrypoint
  // Code size       33 (0x21)
  .maxstack  1
  .locals init ([0] class ConsoleApplication3.InstanceType y)
  IL_0000:  newobj     instance void ConsoleApplication3.InstanceType::.ctor()
  IL_0005:  pop
  IL_0006:  newobj     instance void ConsoleApplication3.InstanceType::.ctor()
  IL_000b:  stloc.0
  IL_000c:  ldloc.0
  IL_000d:  callvirt   instance class ConsoleApplication3.InstanceType ConsoleApplication3.InstanceType::DoSideEffects()
  IL_0012:  pop
  IL_0013:  ldloc.0
  IL_0014:  callvirt   instance class ConsoleApplication3.InstanceType ConsoleApplication3.InstanceType::DoMoreSideEffects()
  IL_0019:  pop
  IL_001a:  call       valuetype [mscorlib]System.ConsoleKeyInfo [mscorlib]System.Console::ReadKey()
  IL_001f:  pop
  IL_0020:  ret
} // end of method Program::Main

Tim McSweeney 9 年前

抱歉拖出这么一个旧帖子,但我遇到了同样的事情,这是我唯一能找到的关于这个问题的讨论。

我对发生的事有预感。这个 [Conditional] 正在取消呼叫 ConditionalMethod() 作为传递给它的参数的任何表达式(根据文档和上面链接的另一个线程)。

我的猜测是 this x.DoSideEffects().DoMoreSideEffects().ConditionalMethod(); 传递为 这 是 x.DoSideEffects().DoMoreSideEffects() 这是尽职的剥离,消除了副作用。

如果我们重写成伪代码 这 作为每种方法的第一个参数,它变得更加清晰:

ConditionalMethod( DoMoreSideEffects( DoSideEffects( x )));