Forum: Ruby eRB <%=

whats eRBs <%= doing in contrast to <%?

Jonas Hartmann wrote:
> whats eRBs <%= doing in contrast to <%?
>
>
= will output the result.

On Wednesday 13 September 2006 20:49, Jonas Hartmann wrote:
> whats eRBs <%= doing in contrast to <%?

Check out the documentation - 
http://www.ruby-doc.org/core/classes/ERB.html

>   <% Ruby code -- inline with output %>
>   <%= Ruby expression -- replace with result %>

Alex

Prints out the result. Aka:

<% puts "Can't see me" %> --> nothing

<%= puts "Can't see me" %> --> Can't see me

Jason

Jonas Hartmann wrote:
> whats eRBs <%= doing in contrast to <%?
>
>
>
the evaluated contents of
<%= %> (e.g. <%= "hello" + @user.name%> )
gets inserted into the rendered html file,
whereas
<%%> (e.g. <%if @user.logged_in?%> Welcome Back! <%else%> Sign up! 
<%end%> )
doesn't go into the eventual html file that gets served to the client...

Gustav Paul
gustav@rails.co.za
itsdEx.com

--
about me:
My greatest achievement was when all the other
kids just learnt to count from 1 to 10,
i was counting (0..9)

   - gustav.paul

A. S. Bradbury wrote:
> On Wednesday 13 September 2006 20:49, Jonas Hartmann wrote:
>> whats eRBs <%= doing in contrast to <%?
> 
> Check out the documentation - http://www.ruby-doc.org/core/classes/ERB.html
> 
>>   <% Ruby code -- inline with output %>
>>   <%= Ruby expression -- replace with result %>
> 
> Alex

great stuff, i am not so familiar with the ruby docs they confuse me
sometimes - sry.

On 9/13/06, Jason Roelofs <jameskilton@gmail.com> wrote:
> <% puts "Can't see me" %> --> nothing
>
> <%= puts "Can't see me" %> --> Can't see me

That's wrong. When rendering an ERB template, those two constructs
would be essentially equivalent. The both do the same thing: print
"Can't see me" to STDOUT and add nothing to the rendered output.

Using puts inside ERB does not put things into the rendered output --
it's not equivalent to PHP's echo/print. You should never need to use
puts or print within ERB (unless your intent is to print diagnostics
out to STDOUT while the ERB is being rendered).

<% %> and <%= %> both evaluate an expression. The difference is that
<%= %> includes the result of the expression (cast to a string using
to_s) in the rendered output. The result of the expression:

   puts "Can't see me"

is nil, since puts always returns nil. nil.to_s is an empty string, so
even with the <%= %> form, nothing is added to the rendered output.

What you want to do instead is just leave off the puts:

   Nothing added: <% "Can't see me" %>
   But printed here: <%= "Can see me" %>

Jacob Fugal

On 9/13/06, Jacob Fugal <lukfugl@gmail.com> wrote:
> it's not equivalent to PHP's echo/print. You should never need to use
> even with the <%= %> form, nothing is added to the rendered output.
>
> What you want to do instead is just leave off the puts:
>
>    Nothing added: <% "Can't see me" %>
>    But printed here: <%= "Can see me" %>
>
> Jacob Fugal
>
>

One thing I've often wondered is how do you output from w/i a "non
output" block...ie in java scriptlets these are equivalent:

<% out.println("hi") %>
<%= "hi" %>

With ERB I've had some (admittedly rare) cases where this would be
useful.  Is it possible?

- rob

On Sep 13, 2006, at 6:05 PM, Rob Sanheim wrote:

>> Using puts inside ERB does not put things into the rendered output --
>> is nil, since puts always returns nil. nil.to_s is an empty  
>>
> - rob
<% _erbout << "hi" %>

Its ugly but it works.

-Ezra

On 9/13/06, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
> <% _erbout << "hi" %>
>
> Its ugly but it works.

You can of course also wrap it in a helper[1] method of your own as
well, to get rid of the ugly. For example:

  def echo(value)
    _erbout << value.to_s
  end

then later in your template:

  <% echo "Hi!" %>

Jacob Fugal

[1] If you take "helper" there literally in the rails sense, you
probably want it in your application_helper.rb file; the same can
apply for any ERB usage using "helper" in a more general sense,
however.

On Sep 13, 2006, at 7:32 PM, Jacob Fugal wrote:

>>
>
>
Actually that doesn't work in a helper. You will get this error:"

undefined local variable or method `_erbout' for #<#<Class:0x358b7c8>:
0x358b7a0>

its because when you call _erbout it takes a second arg that defaults
to  binding. The binding and _erbout are not available within a
helper method.

-Ezra

On 9/13/06, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
>         Actually that doesn't work in a helper. You will get this error:"
>
> undefined local variable or method `_erbout' for #<#<Class:0x358b7c8>:
> 0x358b7a0>
>
> its because when you call _erbout it takes a second arg that defaults
> to  binding. The binding and _erbout are not available within a
> helper method.

Good point, thanks for the pointer. So looks like you're stuck with
the uglies if you really want to do it.

Another option (maybe?) would be to just switch context briefly:

  <%
    # doing stuff here
    # but now I want to print something
  %><%= value %><%
    # continue doing stuff...
  %>

Jacob Fugal

On 9/14/06, Jacob Fugal <lukfugl@gmail.com> wrote:
> > helper method.
>
> Good point, thanks for the pointer. So looks like you're stuck with
> the uglies if you really want to do it.


Can you not just build up a string in the helper method and then return
that?

def echo(value)
  "Something with #{value}"
end