Question

Func<Classification, string> test1 = c => c.Id = "x"; 
Func<Classification, string> test2 = c => { return c.Id = "x";}; 

I’ve worked with lambda’s for nearly a year or so now and fairly reasonable with them, but today I was looking at NBuilder and seen a weird Func that didn’t seem to match the examples. I had play anyway and it checks out but I don’t understand why the above compiles let alone runs. We are doing an assignment and thus the expression doesn’t evaluate to anything, right??? or not

So I thought maybe something I’ve missed related to lambda, so I tried something else:

    [Test]
    public void AmIGoingMad()
    {
        Assert.That(Test(),Is.Null); // not sure what to expect - compile fail?
    }

    public string Test()
    {
        string subject = "";
        return subject = "Matt";
    }

Sure enough AmIGoingMad fails and “Matt” is actually returned.

Why do we have this behavior? Where is this documented? Is it purely a syntactic shortcut?

I feel like I missed something fundamental in my understanding of lambda or even C#.

Feeling dumb.

Answer 1

An assignment statement has a return value–that value is that which was assigned. Even C had this, so you could chain together assignments like the following:

a = b = c = d = 10;

The assignment to d has the return value of 10 which gets assigned to c, and so on.