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Contents
module Alf
module Tools
#
# Provides a handle for implementing a flyweight design pattern on tuples.
#
# This class works hand-in-hand with TupleExpression as it provides a scope
# for their evaluation on tuples.
#
# Example:
#
# handle = TupleHandle.new
# expr = TupleExpression["status > 10"]
# relation.each do |tuple|
# expr.evaluate(handle.set(tuple))
# end
#
class TupleHandle
# Creates a handle instance
def initialize
@tuple = nil
end
# Sets the next tuple to use.
#
# On first call, this method installs the handle as a side effect.
#
# @param [Tuple] tuple the current iterated tuple
# @return [TupleHandle] self
def set(tuple)
build(tuple) if @tuple.nil?
@tuple = tuple
self
end
# Evaluates a tuple expression on the current tuple.
#
# @param [Object] expr a tuple expression (coercions apply)
# @return [Object] the result of evaluting `expr` on self
def evaluate(expr)
TupleExpression.coerce(expr).evaluate(self)
end
private
# Builds this handle with a tuple.
#
# This method should be called only once and installs instance methods on
# the handle with keys of _tuple_.
def build(tuple)
tuple.keys.each do |k|
(class << self; self; end).send(:define_method, k) do
@tuple[k]
end
end
end
end # class TupleHandle
end # module Tools
end # module Alf
Version data entries
5 entries across 5 versions & 1 rubygems