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Versions: 32
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Contents
module Bmg
module Relation
#
# The empty relation, of a given type.
#
# This relation implementation exists mostly for optimization
# purposes, since knowing that a relation is empty allows
# simplifying many expressions.
#
class Empty
include Relation
def initialize(type)
@type = type
end
attr_accessor :type
protected :type=
def each(&bl)
end
def _count
0
end
def to_ast
[ :empty ]
end
def to_s
"(empty)"
end
def inspect
"(empty)"
end
protected ### optimization
def _allbut(type, *args)
Empty.new(type)
end
def _autosummarize(type, *args)
Empty.new(type)
end
def _autowrap(type, *args)
Empty.new(type)
end
def _constants(type, cs)
Empty.new(type)
end
def _extend(type, *args)
Empty.new(type)
end
def _image(type, *args)
Empty.new(type)
end
def _project(type, *args)
Empty.new(type)
end
def _rename(type, *args)
Empty.new(type)
end
def _restrict(type, predicate)
self
end
def _union(type, other, options)
other
end
end # class Empty
end # module Relation
end # module Bmg
Version data entries
32 entries across 32 versions & 1 rubygems