> $a == $b != NaN
>
> really means this:
>
> $a == $b && $b != NaN
>
> But "$a == $b != NaN" is supposed to "[solve] the problem of numerical
> comparisons between non-numeric strings." Well, what if:
>
> $a = 'hello';
> $b = 0;
>
> Doesn't that mean:
>
> "hello" == 0 && 0 != NaN
>
> will evaluate to true?
No. The step you're missing is that the non-numeric string "hello",
when evaluated in a numeric context, produces NaN. So:
"hello" == 0 && 0 != NaN
is:
Nan == 0 && 0 != NaN
which is false.
And in the reverse case:
$a = 0;
$b = 'hello';
then:
$a == $b != NaN
is:
$a == $b && $b != NaN
is:
0 == "hello" && "hello" != NaN
is:
0 == NaN && NaN != NaN
which is false too.
The C<!= NaN> is really only needed to cover the third case:
$a = 'goodbye';
$b = 'hello';
when:
$a == $b != NaN
is:
$a == $b && $b != NaN
is:
"goodbye" == "hello" && "hello" != NaN
is:
NaN == NaN && NaN != NaN
which is false as well.
Damian
