undef value is roughly equivalent
nil in Ruby. It represents the absence of a value. If
strict_variables setting isn’t enabled, variables which have never been
declared have a value of
undef value is useful for testing
whether a variable has been set. Also, you can use it to un-set resource attributes
that have inherited values from a resource
default, causing the attribute to be unmanaged.
The only value in the
Undef data type is the bare word
When used as a boolean,
undef is false.
When interpolated into a string,
undef is converted to the empty
Undef data type
The data type of
Undef. It matches only the
undef, and takes no parameters.
undefin addition to several other data types.
Anytype matches any value, including
Optionaltype wraps one other data type, and returns a type that matches
undefin addition to that type.
Varianttype can accept the
Undeftype as a parameter, which makes the resulting data type match
NotUndeftype matches any value except