Why is the compiler saying a field is never used when it is?

Question

Pursuing perfection so as to catch beaudaciousness (paraphrasing Vince Lombardi), I tried to rid a project of its sole warning, which was: c:\project\nrps\PoisonFoot\releases\6-4-0\hhs\frmPlatypus.cs(103,16): warning CS0169: The private field 'PDQClient.frmPlatypus.scanned' is never used

So I commented out that line:

private bool scanned = false;

...but then I got:

C:\Project\nrps\PoisonFoot\Releases\6-4-0\HHS\frmPlatypus.cs(3390): The name 'scanned' does not exist in the class or namespace 'PDQClient.frmPlatypus'

...in two places (in the same class where it's supposedly unnecessarily defined)

How was I able to hoodwink the compiler without even trying? How can I get rid of the warning without receiving an err?

_"Pursuing perfection ..."_ so upgrade your Visual Studio version... you're 10 years behind. `:)` — gdoron, May 28 '14 at 21:42
-Show- Read the lines where the compiler complains. `scanned` is assigned there, but never read again. — CodeCaster, May 28 '14 at 21:46
possible duplicate of [Suppressing "is never used" and "is never assigned to" warnings in C#](http://stackoverflow.com/questions/3820985/suppressing-is-never-used-and-is-never-assigned-to-warnings-in-c-sharp) — Cᴏʀʏ, May 28 '14 at 21:47
If only I could - we are stuck in the "cave man days" here... — B. Clay Shannon-B. Crow Raven, May 28 '14 at 21:56
Woe on those super-fast close voters. There __was__ enough information to find the answer, and I learned from it!! — TaW, May 29 '14 at 06:56

score 20 · Accepted Answer · answered May 28 '14 at 21:47

20

When csc(the C# compiler) says a field is never used, what it actually means is that you never read from the field. If you only write to a private member field the compiler deduces that the field is redundant. So, I'm gonna assume that in line 3390 of frmPlatypus.cs you are assigning to scanned, not reading from it, and that's why the compiler complains.

Also - line 3390? Really?

answered May 28 '14 at 21:47

Idan Arye

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+1 for _"Also - line 3390? Really?"_. BTW, I have seen worst... – gdoron May 28 '14 at 21:50
Not "redundant" but irrelevant. Its assignment might even be missing from the IL. – Cᴏʀʏ May 28 '14 at 21:52
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What do you mean by "line 3390? Really?" I've worked on files with orders of magnitude more lines than that. In fact, I've seen METHODS with that many lines (and I've never seen the healthcare.gov code). – B. Clay Shannon-B. Crow Raven May 28 '14 at 21:55
I got rid of ALL the code referencing that field - in one place it was assigned "true" and in another place "false" but those states never had any effect on anything else. – B. Clay Shannon-B. Crow Raven May 28 '14 at 22:03
Looks like it's a form class based on the name, if he's using the Form Designer, 3390 lines is not actually that many... – Middas May 28 '14 at 22:19
Yeah, cats here write 3390 LOC before breakfast. – B. Clay Shannon-B. Crow Raven May 29 '14 at 15:12

Why is the compiler saying a field is never used when it is?

1 Answers1