Rubyには、列挙子でやりたいことを実行するための組み込みメソッドがあまりないようですが、独自のメソッドを作成することはできます。これが、Ruby1.9を使用してここで行ったことです。
iter.rb
def get_enums_from_args(args)
args.collect { |e| e.is_a?(Enumerator) ? e.dup : e.to_enum }
end
def build(y, &block)
while true
y << (begin yield; rescue StopIteration; break; end)
end
end
def zip(*args)
enums = get_enums_from_args args
Enumerator.new do |y|
build y do
enums.collect { |e| e.next }
end
end
end
def chain(*args)
enums = get_enums_from_args args
Enumerator.new do |y|
enums.each do |e|
build y do
e.next
end
end
end
end
def multiply(*args)
enums = get_enums_from_args args
duped_enums = enums.collect { |e| e.dup }
Enumerator.new do |y|
begin
while true
y << (begin; enums.collect { |e| e.peek }; rescue StopIteration; break; end )
index = enums.length - 1
while true
begin
enums[index].next
enums[index].peek
break
rescue StopIteration
# Some iterator ran out of items.
# If it was the first iterator, we are done,
raise if index == 0
# If it was a different iterator, reset it
# and then look at the iterator before it.
enums[index] = duped_enums[index].dup
index -= 1
end
end
end
rescue StopIteration
end
end
end
そして、rspecを使用して仕様を作成し、関数をテストして、それらが何をするかを示しました。
iter_spec.rb：
require_relative 'iter'
describe "zip" do
it "zips together enumerators" do
e1 = "Louis".chars
e2 = "198".chars
zip(e1,e2).to_a.should == [ ['L','1'], ['o','9'], ['u','8'] ]
end
it "works with arrays too" do
zip([1,2], [:a, nil]).to_a.should == [ [1,:a], [2,nil] ]
end
end
describe "chain" do
it "chains enumerators" do
e1 = "Jon".chars
e2 = 0..99999999999
e = chain(e1, e2)
e.next.should == "J"
e.next.should == "o"
e.next.should == "n"
e.next.should == 0
e.next.should == 1
end
end
describe "multiply" do
it "multiplies enumerators" do
e1 = "ABC".chars
e2 = 1..3
multiply(e1, e2).to_a.should == [["A", 1], ["A", 2], ["A", 3], ["B", 1], ["B", 2], ["B", 3], ["C", 1], ["C", 2], ["C", 3]]
end
it "is lazily evalutated" do
e1 = 0..999999999
e2 = 1..3
e = multiply(e1, e2)
e.next.should == [0, 1]
e.next.should == [0, 2]
e.next.should == [0, 3]
e.next.should == [1, 1]
e.next.should == [1, 2]
end
it "resulting enumerator can not be cloned effectively" do
ranks = chain(2..10, [:jack, :queen, :king, :ace])
suits = [:clubs, :diamonds, :hearts, :spades]
cards = multiply(suits, ranks)
c2 = cards.clone
cards.next.should == [:clubs, 2]
c2.next.should == [:clubs, 2]
c2.next.should == [:clubs, 3]
c2.next.should == [:clubs, 4]
c2.next.should == [:clubs, 5]
cards.next.should == [:clubs, 6]
end
it "resulting enumerator can not be duplicated after first item is evaluated" do
ranks = chain(2..10, [:jack, :queen, :king, :ace])
suits = [:clubs, :diamonds, :hearts, :spades]
cards = multiply(ranks, suits)
cards.peek
lambda { cards.dup }.should raise_error TypeError
end
end
上記の仕様に示されているように、これらのメソッドは遅延評価を使用します。
また、ここで定義されている、、、および関数の主な弱点は、zipこれらの新しい列挙子が依存する列挙型引数を複製するコードを記述していないため、結果の列挙子を簡単に複製または複製できないことです。うまく機能させるには、おそらくモジュールのサブクラスを作成するか、モジュールを含むクラスを作成する必要があります。chainmultiplyEnumeratorEnumerabledup