When the null conditional operator short-circuits, does it still evaluate method arguments?

Question

The null conditional operator can be used to skip method calls on a null target. Would the method arguments be evaluated or not in that case?

For example:

myObject?.DoSomething(GetFromNetwork());

Is GetFromNetwork called when myObject is null?

Garrow

Answer 1

They will not be evaluated.

class C
{
    public void Method(int x)
    {
        Console.WriteLine("Method");
    }
}

static int GetSomeValue()
{
    Console.WriteLine("GetSomeValue");
    return 0;
}

C c = null;
c?.Method(GetSomeValue());

This does not print anything. Resharper marks the evaluation of GetSomeValue()as dead code:

Garrow

Answer 2

myObject?.Method();

is basically equivalent to

var temp = myObject;
if (temp != null) {
    temp.Method();
}

You see that no argument can be evaluated if myObject is null.

Note that if you replaced myObject by

Leanaleanard

They are not equivalent. Specifically, the former evaluates object only once, the latter twice if non-null. Since they're not equivalent, no conclusions should be drawn from it. – Norikonorina

@hvd They are. It is stated as this even in the specs (literally!). And since it is a variable, there is no double evaluation. github.com/ljw1004/csharpspec/blob/gh-pages/… – Leanaleanard

They are not in general, as stated in the very specs you link to: "except that P is evaluated only once.", later "except that P is evaluated only once.", yet later "except that P is evaluated only once.", finally "Except that a.b and a.b[0] are evaluated only once." and "except that a.b and a.b[0] are evaluated only once." Yes, for a local variable, double evaluation does not change the results. The part that this is the only exception would be a good addition to your answer, IMO. – Norikonorina