C＃？。条件运算符

Question

我有条件

if (driver?.VistrackId == 555)

它等效（在 IL 代码中，而不是 C# 代码中）：

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

对吗？

Answer 1

没错。这 ”？”检查是否为空，如果不为空，则“.”继续审问对象

Answer 2

不完全是

It's better Since this notation is thread safe

见Null-conditional Operators on MSDN。

Answer 3

此代码生成以下 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

代码 == null

var driver = new {VistrackId = 1};


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

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:  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

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