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Boolean functions

$boolean()

Signature: $boolean(arg)

Casts the argument to a Boolean using the following rules:

Argument type	Result
Boolean	unchanged
string: empty	false
string: non-empty	true
number: 0	false
number: non-zero	true
null	false
array: empty	false
array: contains a member that casts to true	true
array: all members cast to false	false
object: empty	false
object: non-empty	true
function	false

$not()

Signature: $not(arg)

Returns Boolean NOT on the argument. arg is first cast to a boolean

$exists()

Signature: $exists(arg)

Returns Boolean true if the arg expression evaluates to a value, or false if the expression does not match anything (e.g. a path to a non-existent field reference).