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Contents
#--
# Credit goes to Gavin Sinclair.
#++
module Enumerable
# Enumerable#one? returns +true+ if and only if <em>exactly one</em>
# element in the collection satisfies the given predicate.
#
# If no predicate is provided, Enumerable#one? returns +true+ if
# and only if <em>exactly one</em> element has a true value
# (i.e. not +nil+ or +false+).
#
# [].one? # false
# [nil].one? # false
# [5].one? # true
# [5,8,9].one? # false
# (1...10).one? { |n| n == 5 } # true
# (1...10).one? { |n| n < 5 } # false
#
def one? # :yield: e
matches = 0
if block_given?
self.each do |e|
if yield(e)
matches += 1
return false if matches > 1
end
end
return (matches == 1)
else
one? { |e| e }
end
end
end
# _____ _
# |_ _|__ ___| |_
# | |/ _ \/ __| __|
# | | __/\__ \ |_
# |_|\___||___/\__|
#
=begin test
require 'test/unit'
class TCEnumerable < Test::Unit::TestCase
def test_one?
a = [nil, true]
assert( a.one? )
a = [true, false]
assert( a.one? )
a = [true, true]
assert( ! a.one? )
a = [true, 1]
assert( ! a.one? )
a = [1, 1]
assert( ! a.one? )
end
end
=end
Version data entries
26 entries across 26 versions & 1 rubygems