diff options
| -rw-r--r-- | railties/guides/source/active_support_overview.textile | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/railties/guides/source/active_support_overview.textile b/railties/guides/source/active_support_overview.textile index 715e5c17d8..30a593a0d7 100644 --- a/railties/guides/source/active_support_overview.textile +++ b/railties/guides/source/active_support_overview.textile @@ -51,6 +51,40 @@ The method +present?+ is equivalent to +!blank?+: assert @response.body.present? # same as !@response.body.blank? </ruby> +h4. +duplicable?+ + +A few fundamental objects in Ruby are singletons. For example, in the whole live of a program the integer 1 refers always to the same instance: + +<ruby> +1.object_id # => 3 +Math.cos(0).to_i.object_id # => 3 +</ruby> + +Hence, there's no way these objects can be duplicated through +dup+ or +clone+: + +<ruby> +true.dup # => TypeError: can't dup TrueClass +</ruby> + +Some numbers which are not singletons are not duplicable either: + +<ruby> +0.0.clone # => allocator undefined for Float +(2**1024).clone # => allocator undefined for Bignum +</ruby> + +Active Support provides +duplicable?+ to programmatically query an object about this property: + +<ruby> +"".duplicable? # => true +false.duplicable? # => false +</ruby> + +By definition all objects are +duplicable?+ except +nil+, +false+, +true+, symbols, and numbers. + +WARNING. Using +duplicable?+ is discouraged because it depends on a hard-coded list. Classes have means to disallow duplication like removing +dup+ and +clone+ or raising exceptions from them, only +rescue+ can tell. + + h4. +metaclass+ The method +metaclass+ returns the singleton class on any object: |