ruby on rails - yield and provide() inside template

Question

Could anyone give clear explanation on how provide() works inside the view ? I have read official documentation but what really bothers me is this, if I define in the beginning of a template

<% provide(:title, 'Help') %>

and then later I have this line of code

<%= yield :title %> 

what really happens in the background ? I know that yield is supposed to call code block. What would be code block in this context?

Answer 1

provide stores a block of markup in an identifier for later use. In this case, 'Help' in the symbol :title. The provide is enclosed in <% %> to indicate it is executing this code and not printing out in the view.

yield in this case just spits that block back out. The yield is enclosed in <%= %> to indicate it is being printed out into the view.

Think of it as setting a variable and printing out a variable.

See: http://api.rubyonrails.org/classes/ActionView/Helpers/CaptureHelper.html#method-i-provide for more information. Note that provide is really a wrapper for content_for so that's where the good stuff is in that link.