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Re^3: elsif statement not being evaluated

by afoken (Abbot)
on Nov 18, 2012 at 08:35 UTC ( #1004386=note: print w/replies, xml ) Need Help??

in reply to Re^2: elsif statement not being evaluated
in thread elsif statement not being evaluated

Happens to everyone using C or languages inheriting or stealing from C. But you can make the compiler / interpreter complain loudly if you make sure the constant is on the left side of the operator:

if ($answer=42) { # $answer is now always 42 ... } if (42=$answer) { # "Can't modify constant item in scalar assignment" ... }

This won't help when you compare two variables, but in your case, the variables $an1 and $an2 aren't variable, but constant. So make them constant, either by using Readonly or by using constant:

use Readonly; Readonly my $fortytwo => 42; # note: =>, not = ... if ($fortytwo=$answer) { # "Modification of a read-only value attempte +d" ... }
use constant FORTYTWO => 42; # note: =>, not = ... if (FORTYTWO=$answer) { # "Can't modify constant item in scalar assign +ment" ... }

Or, in this trivial case, get rid of $an1 and $an2 and use 1 and 2.

I prefer Readonly over constant, because Readonly just makes the variables readonly, with no surprises, whereas constant (ab)uses the perl optimizer and implements the constants as functions returning a constant value. This has some nasty side effects documented in Readonly.


Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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[stevieb]: choroba my GPS home device is done, at least prototype v1 is. I'm just making sure all of my code does what it says now
[stevieb]: I test/prototype code on my Pi, then I migrate it over to Arduino when it's ready (if that's a better platform for what I'm doing). The whole RPi stuff was for learning at first, then it snowballed. I'm just trying to get my in-house CI...
[stevieb]: ...done, which obviously requires a specific hardware setup.
[stevieb]: I don't write tests for the lower-level distributions (ie. ICs, sensors etc) within those distributions, I have all tests in a master distribution which encompasess all of the sub-modules

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