Can a journal entry id be 0?

[purplecat]

For Bug 2152 I've found I need to create a subroutine that checks whether a form element refers to a valid entry in the user's journal separately from the various subroutines for actually saving it as a sticky.

If a journal entry id can never be zero then this subroutine could return the id number if it is valid and 0 otherwise. In that case the subroutine can replace duplicate code in at least two places, but obviously if an entry can be 0 then the subroutine had better just return 0 or 1.

Comments

[mark]

No, ids should never be 0.

Also, the typical "error" result is undef. You can use 0 if it's relevant, but Perl typically uses undef as the "something went wrong" result.

[purplecat]

Thanks! I'll return undef then!

[sophie]

BTW, you may already know this, but this bit me the first time I used undef, so I'll leave this here in case you or anybody else watching runs into it...

If you want to test for a variable being undef, you can't do if ( $var == undef ) or similar. You'd need to use if ( ! defined( $var ) ). That's because undef isn't actually a value you can compare against. Rather annoying, but there you go. Hopefully this staves off any confusion in this regard :)

[mark]

Style note: minimize extraneous paranthesis. Prefer this format:

if (! defined $var )

But if you're doing that, you should probably use unless.

[purplecat]

I didn't know that! Or, if I did, I'd forgotten - thanks!

[purplecat]

Quick follow up question. Since I'm having to validate the form entries before calling a second subroutine to store the data, is it preferable to revalidate in the body of the second subroutine, or to assume that the input will always be valid by the time it gets there? i.e. should I err on the side of safety or efficiency?

[mark]

Every sub should check its inputs. While you may be the only person calling it and it may be extraneous, in six months someone else might decide to call your function and if they pass bad inputs, you're in trouble.

The only exception to this is if you have a locally scoped closure (i.e., my $x = sub { ... };) then, since nobody else can call it except you, validating inputs is not something to worry about.

[purplecat]

I'll revalidate then, thanks!