C # Zero Spread - Where does the magic happen?

Question

Zero distribution is a very nice feature, but where and how real magic happens. Where frm?.Close()does it change to if(frm != null) frm.Close();- does it really change to this type of code?

Answer 1

This is done by the compiler. It does not change frm?.Close()to if(frm != null) frm.Close();in terms of rewriting the source code, but it emits an IL bytecode that checks for null.

Take the following example:

void Main()
{
    Person p = GetPerson();
    p?.DoIt();
}

Compiles:

IL_0000:  ldarg.0     
IL_0001:  call        UserQuery.GetPerson
IL_0006:  dup         
IL_0007:  brtrue.s    IL_000B
IL_0009:  pop         
IL_000A:  ret         
IL_000B:  call        UserQuery+Person.DoIt
IL_0010:  ret         

What can be read as:

call - GetPerson() - .
dup - ()
brtrue.s - . , - ( ), IL_000B

( null)
pop - ( , Person)
ret -

(.. )
call - DoIt() ( GetPerson).
ret -

:

Person p = GetPerson();
if (p != null)
    p.DoIt();

IL_0000:  ldarg.0     
IL_0001:  call        UserQuery.GetPerson
IL_0006:  stloc.0     // p
IL_0007:  ldloc.0     // p
IL_0008:  brfalse.s   IL_0010
IL_000A:  ldloc.0     // p
IL_000B:  callvirt    UserQuery+Person.DoIt
IL_0010:  ret         

, ?., .

:

void Main()
{
    Person p = GetPerson();
    p.DoIt();
}

IL_0000:  ldarg.0     
IL_0001:  call        UserQuery.GetPerson
IL_0006:  callvirt    UserQuery+Person.DoIt
IL_000B:  ret         

Answer 2

?

, , IL, #. IL-, #, .