Is it OK not to handle returned value of a C# method? What is good practice in this example?

Question

Out of curiosity...what happens when we call a method that returns some value but we don\'t handle/use it? And we also expect that sometimes this returned value could be rea

Answer 1

The returned value (or reference, if it's a reference type) is pushed onto the stack and then popped off again.

No biggy.

If the return value isn't relevant, you can safely do this.

But be sure that it isn't relevant, just in case.

Here's some code:

    static string GetSomething()
    {
        return "Hello";
    }

    static void Method1()
    {
        string result = GetSomething();
    }

    static void Method2()
    {
        GetSomething();
    }

If we look at the IL:

Method1:

.locals init ([0] string result)
IL_0000:  nop
IL_0001:  call       string ConsoleApplication3.Program::GetSomething()
IL_0006:  stloc.0
IL_0007:  ret

Method2:

IL_0000:  nop
IL_0001:  call       string ConsoleApplication3.Program::GetSomething()
IL_0006:  pop
IL_0007:  ret

Exactly the same number of instructions. In Method1, the value is stored in the local string result (stloc.0), which is deleted when it goes out of scope. In Method2, the pop operation simply removes it from the stack.

In your case of returning something 'really big', that data has already been created and the method returns a reference to it; not the data itself. In Method1(), the reference is assigned to the local variable and the garbage collector will tidy it up after the variable has gone out of scope (the end of the method in this case). In Method2(), the garbage collector can get to work, any time after the reference has been popped from the stack.

By ignoring the return value, if it really isn't needed, the garbage collector can potentially get to work sooner and release any memory that's been assigned. But there's very little in it (certainly in this case), but with a long running method, hanging onto that data could be an issue.

But far-and-away the most important thing is to be sure that the return value that you're ignoring isn't something that you should be acting on.

Answer 2

The returned value is thrown away if not used, but it is created. It is perfectly reasonable not to use it ( although you should be ceratin that this is the right thing to be doing ), but if it takes a lot of resource to create, then this is wasted.

You may want to consider whether another method would be a better options, that doesn't create the return object at all.

Answer 3

EDIT: Softened the language very slightly, and clarified.

It's rarely a good idea to ignore the return value, in my experience - at least in cases where the return values are there to convey new information instead of simply being for convenience.

One example where I've seen it be okay:

int foo;
int.TryParse(someText, out foo);

// Keep going

Here foo will be 0 if either someText contained "0", or it couldn't be parsed. We may not care which was the case in which case the return value of the method is irrelevant to us.

Another example is in a dictionary - suppose you're trying to count the number of occurrences of each string. You can use:

int count;
dictionary.TryGetValue(word, out count);
dictionary[word] = count + 1;

If the word wasn't in the dictionary to start with, that's equivalent to there being a count of 0 - which is what will already happen as a result of calling TryGetValue.

As a counter-example, ignoring the value returned by Stream.Read (and assuming that it's managed to read all the data you asked for) is a common mistake.

If you don't need the return value and it will have taken a lot of effort to compute, it may be worth looking for something which will achieve the same desired side-effects without the extra computation - but there's no extra performance implication. I'd be more worried about the correctness of ignoring a return value than the performance.

EDIT: Other examples where it's okay to ignore the return value:

• Some fluent interfaces, including StringBuilder; while StringBuilder.Append(x).Append(y); uses the first return value for the second call, very often the return value of a call will be ignored, e.g. when appending in a loop
• Some collection calls can give return values which are sometimes ignored - e.g. HashSet<T>.Add which indicates whether the value was actually added, or was already present. Sometimes you just don't care.

But for the vast majority of the time, ignoring the return value of a method indicates that it's doing more than you need it to.

Answer 4

All this talk about whether it is okay to ignore returned types is not needed, we do it all the time anyway in C#. Lots of functions you use as if they are returning void are not returning void. Think about a common function like Button1.Focus()

Did you know that the .Focus() function returns a bool value? It returns true if it succeeded in focusing on the control. So you could test it as a bool by saying:

if (Button1.Focus == true) MessageBox.Show("Button Focused successfully."); else MessageBox.Show("Could not focus on the button, sorry.");

But normally, you don't do this. You just say: Button1.Focus();

and you're done. I could give a hundred other examples where we ignore return values, like when a function runs but also returns a reference to something it created, but you don't care about the reference, you just wanted it to do the action (or you just want to simply check whether there is a reference or if it is null)

The point is, we ignore return values all the time, even if you don't know it.

Answer 5

It's totally fine to ignore the return value.

However. The architectural design is, IMHO, not good. An insert method should not return anything at all (other than MAYBE true or false on success or failure). If one would need to get a new, updated, dataset then one should ask for it, i.e call some other method to do so.

Answer 6

To give a different perspective on things, I think that method should be redesigned. Take a look at the Command-Query separation.

Also, it's rarely a good idea to silently ignore a return value. Readers of the code might not have the original context of the author. They might think he just forgot to use it. If the return value is not important, better be explicit about this decision:

var ignoredReturnValue = InsertIntoDB(...);

Interestingly, Nemerle actually gives you a warning if you ignore a return value. To not get the warning, you have to be explicit about your decision and write:

_ = InsertIntoDB(...);