How can I tell the difference between a variable whose value is null and
a variable which is not set?
// cannot use === null:
ket% php -r '$null = null; var_dump(null === $null);'
bool(true)
ket% php -r 'var_dump(null === $unset);' bool(true)
ket%
// - cannot use isset() either:
ket% php -r '$null = null; var_dump(isset($null));' bool(false)
ket% php -r 'var_dump(isset($unset));' bool(false)
ket%
Although this is a good problem to lose time for I think it is pointless. Since assigning the null constant to a var is making PHP to pretend like it never existed.
Is this not the point?
Without this feature I can think many cases that isset or is_null would be useless.
You could always assign to something the empty string '' and use empty() to check it as an alternative.
BTW what are you trying to do?
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Thodoris