强制转换为Func vs new Func？

Question

以下两种说法有什么区别吗？他们都工作。

if (((Func<bool>)(()=>true))()) { .... }; 
if (new Func<bool>(()=>true)()) { .... }; 

Answer 1

不，它们都编译到完全相同的IL。

更容易看到实际上是否给予lambda body一些依赖于状态的东西 - 否则编译器会为每个lambda缓存一个委托实例。但是，例如：

using System; 

class Test 
{ 
    bool value = DateTime.Now.Hour == 10; 

    void Cast() 
    { 
     if (((Func<bool>)(() => value))()) 
     { 
      Console.WriteLine("Yes"); 
     } 
    } 

    void New() 
    { 
     if (new Func<bool>(() => value)()) 
     { 
      Console.WriteLine("Yes"); 
     } 
    } 

    static void Main() 
    { 
     new Test().Cast(); 
     new Test().New(); 
    } 
} 

现在IL为Cast是：

.method private hidebysig instance void Cast() cil managed 
{ 
    // Code size  39 (0x27) 
    .maxstack 2 
    .locals init (bool V_0) 
    IL_0000: nop 
    IL_0001: ldarg.0 
    IL_0002: ldftn  instance bool Test::'<Cast>b__0'() 
    IL_0008: newobj  instance void class [mscorlib]System.Func`1<bool>::.ctor(object, 
                       native int) 
    IL_000d: callvirt instance !0 class [mscorlib]System.Func`1<bool>::Invoke() 
    IL_0012: ldc.i4.0 
    IL_0013: ceq 
    IL_0015: stloc.0 
    IL_0016: ldloc.0 
    IL_0017: brtrue.s IL_0026 
    IL_0019: nop 
    IL_001a: ldstr  "Yes" 
    IL_001f: call  void [mscorlib]System.Console::WriteLine(string) 
    IL_0024: nop 
    IL_0025: nop 
    IL_0026: ret 
} // end of method Test::Cast 

和IL为New是：

.method private hidebysig instance void New() cil managed 
{ 
    // Code size  39 (0x27) 
    .maxstack 2 
    .locals init (bool V_0) 
    IL_0000: nop 
    IL_0001: ldarg.0 
    IL_0002: ldftn  instance bool Test::'<New>b__1'() 
    IL_0008: newobj  instance void class [mscorlib]System.Func`1<bool>::.ctor(object, 
                       native int) 
    IL_000d: callvirt instance !0 class [mscorlib]System.Func`1<bool>::Invoke() 
    IL_0012: ldc.i4.0 
    IL_0013: ceq 
    IL_0015: stloc.0 
    IL_0016: ldloc.0 
    IL_0017: brtrue.s IL_0026 
    IL_0019: nop 
    IL_001a: ldstr  "Yes" 
    IL_001f: call  void [mscorlib]System.Console::WriteLine(string) 
    IL_0024: nop 
    IL_0025: nop 
    IL_0026: ret 
} // end of method Test::New 

正如你可以看到，他们是相同的除了调用ldftn，它只是使用适当的编译器生成的方法。