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### Re^4: Burned by precedence rules (== true)

by demerphq (Chancellor)
 on Dec 30, 2008 at 19:50 UTC ( #733329=note: print w/replies, xml ) Need Help??

in reply to Re^3: Burned by precedence rules (== true)
in thread Burned by precedence rules

I'm sure i shouldnt say this, but more than once I have written

```if ( !\$x == !\$y ) { ... }
if ( !\$x != !\$y ) { ... }

which I think is a fair exception to your rule. I kinda view ! and !! as "boolean constructors", and so long as both sides of your (in)equality are guaranteed to be a "boolean" obtained one of these constructors you can compare them.

But I'm really just nit-picking. :-)

---
\$world=~s/war/peace/g

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Re^5: Burned by precedence rules (== true)
by ikegami (Pope) on Dec 30, 2008 at 20:09 UTC

There's a logical operator for that: xor

```if ( !\$x == !\$y) ) # bool(\$x) == bool(\$y)
if ( !\$x != !\$y  ) # bool(\$x) != bool(\$y)
can be written as
```if ( !(\$x xor \$y) ) # bool(\$x) == bool(\$y)
if (   \$x xor \$y  ) # bool(\$x) != bool(\$y)

Unforunately, both sets have readability issues.

In Perl 6 we can use positive boolean context, which helps readability a little:
```if ?\$x == ?\$y {...}
if ?\$x != ?\$y {...}
We can use junctions, which again helps the different case more than the same case:
```if not \$x ^ \$y {...}
if \$x ^ \$y {...}
or if you prefer:
```if !one(\$x,\$y) {...}
if one(\$x,\$y) {...}
That's probably enough ways to do it...

Nah. Clearly this demonstrates the utility of a few "Boolean comparison" operators:

```    if \$isFree ?= \$isEasy
if \$isOne !?= \$isOther

or  die "Inconsistent state";

system \$verifyUser
or   die "You are not just either a User or an Admin";

;)

- tye

Ah yes, scalar xor, i always forget about it. Personally the !\$x == !\$y makes more sense to me than !(\$x xor \$y). But whatever.

---
\$world=~s/war/peace/g

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