.net - ConditionalAttribute 应该去掉整行，还是只去掉方法调用？

Question

根据 ConditionalAttribute 上的文档类(class):

Applying ConditionalAttribute to a method indicates to compilers that a call to the method should not be compiled into Microsoft intermediate language (MSIL) unless the conditional compilation symbol that is associated with ConditionalAttribute is defined.

对我来说，这就是 Conditional属性仅改变单个方法调用级别的行为。但请考虑以下代码片段:

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 Debug 和 Release 版本的输出:

调试发布
副作用!副作用!
副作用更大!副作用更大!
条件方法运行。
副作用!
副作用更大!
条件方法运行。

这种行为是否在某处指定？ 我原以为两个版本都应该具有相同的输出，除了读取“条件方法运行”的行。

Answer 1

有趣的功能:-) 我从来没有注意到。

我看了一下IL。这并不能解释行为(编译过程)，但我相信它无论如何都记录了结果。

整个 C# 代码行在 IL 中显然被遗漏了:

在DEBUG编译一个新对象
创建(x 变量)，存储
在位置 0 并加载。然后
三种方法都适用
依次:DoSideEffects(),
DeMoreSideEffects() 和
条件方法()

在 RELEASE 编译中，变量仍然被创建，但由于不需要它，它立即被弹出。相反，y 变量存储在位置 0 并加载。

对我来说，这真的是一个错误。似乎可以只排除 IL 中的 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