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Section 8.1.2.1: |
This class provides a nil value for a container element and a nil test. The bit-pattern used to represent the 'nil' value is determined by the class itself if it derives from $NIL or is identically void
It should be noted that this cannot be a partial class because of the rule that a call into a partial class cannot be made from within another partial class.
This operation is provided to return a 'nil' value - one which is distinguished by not being a valid bit-pattern for representation of objects of that class.
elt_nil | : ETP |
This is vacuously true since a result is always provided - even if nil!
The auxiliary function typeof is defined in Secyion 6.9.
This routine returns a hash value for the given item, using the hash routine defined in the class of item (if one is defined), otherwise it uses the system defined hash function.
This predicate returns true when its argument has the value nil - which, from the definition above may be the value void (see the vdm below for the specification of this)
is_elt_nil | ( |
item : ETP | |
) : BOOL |
Note that the argument type in this formal signature is an optional one - signifying in Sather terms that the argument may be void!
Since the argument to a call of this predicate may be nil then this is vacuously true.
This predicate returns true if and only if either the type of item defines a nil value and item has that value or item is void.
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Keith
Hopper. Page last modified: Wednesday, 24 May 2000. |
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