Call By Sharing

厳密にいうとRubyは値を渡している、しかしながらオブジェクトの参照値を渡す場合、例にあったように破壊的なメソッドで参照先を変更することができる。ほかにも例をあげると、Hashの内部を変更した場合、呼び出し元の変数も変更される。

Strictly speaking, Ruby is passing by reference. However, what Ruby is passing is reference value of an object so that you can modify the object which the reference value is pointing using Ruby's destructive method (= methods ending with !). Another example is when you modify a Hash value as follows.

>>  a = {b:'c'}
=> {:b=>"c"}
>> def foo(d); d[:b] = 'C'; end
=> nil
>> foo(a)
=> "C"
>> a
=> {:b=>"C"}

よって厳密には「Pass by reference value, Call by sharing」(http://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_sharing) と呼んだ方が正しいのだが、本書では「オブジェクトを参照で渡す」、といったもう少し抽象的な用語をdRubyとの対比として用いている。

Technically speaking "Call By Sharing", or "Call By Object Sharing" (http://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_sharing) are more correct term, but I wil use the word "Pass by reference" as a more generic meaning which are easier to compare with how dRuby works.

newbamboo/call_by_sharing.md