From: Justin Collins <justincollins@...>
Date: 2008-01-18T06:33:09+09:00
Subject: Re: Ruby syntax in "respond_to do |format| line -- can clari

Joshua Beall wrote:
> Andrew Stewart wrote:
>   
>> On 17 Jan 2008, at 16:21, Joshua Beall wrote:
>> So if you look at your block again:
>>
>>    do |format|
>>      format.html
>>      format.xml
>>    end
>>
>> ...and you imagine executing it as a method, the block variable,
>> format, should look like a method argument.  Accordingly it is set to
>> the responder object passed in by the line:
>>
>>    block.call(responder)
>>     
>
> Ok, I think I'm with you.  Correspondingly that would mean that I can 
> replace this
>
>     respond_to do |format|
>       format.html # index.html.erb
>       format.xml  { render :xml => @posts }
>     end
>
> With this:
>
>     responder = Responder.new(self)
>     responder.html
>     responder.xml { render :xml => @posts}
>     responder.respond
>
> And it should work.  And indeed it does.  However, there are still 
> somethings I don't understand.  Why can't I do this?
>
>     responder = Responder.new(self)
>     responder.html
>     responder.xml( { render :xml => @posts} )
>     responder.respond
>
> If I do that, I get the error (point to the line where I added 
> parentheses):
>
> posts_controller.rb:9: syntax error, unexpected tSYMBEG, expecting kDO 
> or '{' or '('
>
> It's complaining about the symbol :xml.
>   
In this case { render :xml => @posts} is being interpreted as a Hash, not a block and that is messing things up for you. 

Ruby doesn't seem sure about how it should parse this for you. It could be

{render(:xml) => @posts}

or 

{render(:xml => @posts)} #throws a different error

In any case, it still thinks it is a Hash.

-Justin