Any way to have visual studio ignore a a compile error for using an unassigned object?

Question

I have code that basically looks like this (it isn't actually object, but rather a custom class):

object thing
try {
  thing = new object();
    ......

} catch { stuff }
finally {
  if (thing != null) { some clean up code }

But VS is not letting me do this because it says I am referencing an unassigned variable. I am well aware it could be unassigned when this code is run, which is why the null check is there. I don't want to instantiate the object outside of the try block because it does a fair bit and could throw an exception, and I would prefer against wrapping the whole thing in another try/catch block just so I can instantiate it up there. Is there something else I can do?

Similar question: [C# error: Use of unassigned local variable](http://stackoverflow.com/questions/297471/why-do-i-get-this-error-creating-returning-a-new-struct) — Devendra D. Chavan, Feb 22 '12 at 12:30

score 11 · Accepted Answer · answered Feb 22 '12 at 12:28

11

"Unassigned" isn't the same as "null". Your code is simply invalid - you need to fix it.

It's very easy here - just initialize the variable to null to start with:

object thing = null;

Now it will definitely have a value (a null reference) so you're allowed to read from it in the finally block.

The point is that local variables cannot be read before the point at which the compiler can prove that a value (whether null or not) has definitely been assigned. Effectively, local variables don't have "default values".

(Mind you, I'd normally use IDisposable for clean-up code, along with a using statement.)

answered Feb 22 '12 at 12:28

Jon Skeet

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I was unaware unassigned and null were two distinctive states, thank you. You're right about the IDisposable though, this class needs one, and it's simply on my very long list of things to do still – cost Feb 22 '12 at 12:38
1

This has been thoroughly explained here: http://stackoverflow.com/a/8933935/641530 – Ernesto Feb 22 '12 at 22:00

CodesInChaos · Answer 2 · 2012-02-22T12:36:44.693

6

No, you can't disable that compiler error. But why don't you just initialize the variable?

object thing = null;

Unlike fields, local variables don't get initialized to null automatically. They are uninitialized, which is a special state, distinct from being null.

edited Feb 22 '12 at 12:36

answered Feb 22 '12 at 12:28

CodesInChaos

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score 4 · Answer 3 · edited May 23 '17 at 11:59

4

Just do

object thing = null;

and the compiler will be placated.

For background on why the compiler complains about this, see this Eric Lippert answer, whence:

The reason this is illegal in C# is because using an unassigned local has high likelihood of being a bug.

edited May 23 '17 at 11:59

Community

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answered Feb 22 '12 at 12:28

AakashM

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FWIW, it is illegal in Java as well. – Thilo Feb 22 '12 at 12:30

score 2 · Answer 4 · answered Feb 22 '12 at 12:29

2

how about:

    object thing = null;

answered Feb 22 '12 at 12:29

thumbmunkeys

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score 1 · Answer 5 · answered Feb 22 '12 at 12:29

1

What is wrong with just setting to to null initially?

object thing = null;
try {
  thing = new object();
    ......

} catch { stuff }
finally {
  if (thing != null) { some clean up code }

answered Feb 22 '12 at 12:29

Thilo

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score 1 · Answer 6 · answered Feb 22 '12 at 12:29

1

Just assign null to begin with:

object thing = null; // <-- That's assignment enough
try {
  thing = new object();
  ......
} catch { stuff }
finally {
  if (thing != null) { some clean up code }
}

answered Feb 22 '12 at 12:29

JimmiTh

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score 1 · Answer 7 · answered Feb 22 '12 at 12:29

1

Why not try object thing = null; as first line ?

answered Feb 22 '12 at 12:29

montardon

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score 1 · Answer 8 · answered Feb 22 '12 at 12:30

1

change your code to this and it should work ok

object thing = null;
try {
  thing = new object();
    ......

} catch { stuff }
finally {
  if (thing != null) { some clean up code }

answered Feb 22 '12 at 12:30

Ben Robinson

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Any way to have visual studio ignore a a compile error for using an unassigned object?

8 Answers8