C＃ ？。 條件運算符

Question

我有病

if (driver?.VistrackId == 555)

它等效（在IL代碼中，不是C＃代碼中）：

if (driver != null && driver.VistrackId == 555)

對？

Answer 1

不完全是

更好，因為這種表示法是線程安全的

請參閱MSDN上的空條件運算符 。

Answer 2

沒錯 “？” 檢查是否為空，如果不為空，則檢查“。” 繼續對物體的訊問

Answer 3

此代碼生成以下IL

var driver = new {VistrackId = 1};

if (driver?.VistrackId == 555)
{
    Console.WriteLine("?. operator");
}

IL：

IL_0000:  nop         
IL_0001:  ldc.i4.1    
IL_0002:  newobj      <>f__AnonymousType0<System.Int32>..ctor
IL_0007:  stloc.0     // driver
IL_0008:  ldloc.0     // driver
IL_0009:  brtrue.s    IL_000E
IL_000B:  ldc.i4.0    
IL_000C:  br.s        IL_001B
IL_000E:  ldloc.0     // driver
IL_000F:  call        <>f__AnonymousType0<System.Int32>.get_VistrackId
IL_0014:  ldc.i4      2B 02 00 00 
IL_0019:  ceq         
IL_001B:  stloc.1     
IL_001C:  ldloc.1     
IL_001D:  brfalse.s   IL_002C
IL_001F:  nop         
IL_0020:  ldstr       "?. operator"
IL_0025:  call        System.Console.WriteLine
IL_002A:  nop         
IL_002B:  nop         
IL_002C:  ret    

代碼== null

var driver = new {VistrackId = 1};


if (driver != null && driver.VistrackId == 555)
{
    Console.WriteLine("== null");
}

白介素

IL_0000:  nop         
IL_0001:  ldc.i4.1    
IL_0002:  newobj      <>f__AnonymousType0<System.Int32>..ctor
IL_0007:  stloc.0     // driver
IL_0008:  ldloc.0     // driver
IL_0009:  brfalse.s   IL_001A
IL_000B:  ldloc.0     // driver
IL_000C:  callvirt    <>f__AnonymousType0<System.Int32>.get_VistrackId
IL_0011:  ldc.i4      2B 02 00 00 
IL_0016:  ceq         
IL_0018:  br.s        IL_001B
IL_001A:  ldc.i4.0    
IL_001B:  stloc.1     
IL_001C:  ldloc.1     
IL_001D:  brfalse.s   IL_002C
IL_001F:  nop         
IL_0020:  ldstr       "== null"
IL_0025:  call        System.Console.WriteLine
IL_002A:  nop         
IL_002B:  nop         
IL_002C:  ret         

它們略有不同