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Diffstat (limited to 'railties')
| -rw-r--r-- | railties/guides/source/active_support_overview.textile | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/railties/guides/source/active_support_overview.textile b/railties/guides/source/active_support_overview.textile index 4fa7a85464..f9a2f5f963 100644 --- a/railties/guides/source/active_support_overview.textile +++ b/railties/guides/source/active_support_overview.textile @@ -829,6 +829,32 @@ You can pick a random element with +rand+: shape_type = [Circle, Square, Triangle].rand </ruby> +h4. Options Extraction + +When the last argument in a method call is a hash, except perhaps for a +&block+ argument, Ruby allows you to omit the brackets: + +<ruby> +User.exists?(:email => params[:email]) +</ruby> + +That syntactic sugar is used a lot in Rails to avoid positional arguments where there would be too many, offering instead interfaces that emulate named parameters. In particular it is very idiomatic to use a trailing hash for options. + +If a method expects a variable number of arguments and uses <tt>*</tt> in its declaration, however, such an options hash ends up being an item of the array of arguments, where kind of loses its role. + +In those cases, you may give an options hash a distinguished treatment with +extract_options!+. That method checks the type of the last item of an array. If it is a hash it pops it and returns it, otherwise returns an empty hash. + +Let's see for example the definition of the +caches_action+ controller macro: + +<ruby> +def caches_action(*actions) + return unless cache_configured? + options = actions.extract_options! + ... +end +</ruby> + +This method receives an arbitrary number of action names, and an optional hash of options as last argument. With the call to +extract_options!+ you obtain the options hash and remove it from +actions+ in a simple and explicit way. + h4. Conversions h5. +to_sentence+ |