why does this comment create a compile error

rubyonrails-talk
1

there is a line displayed within <pre>

<%= h @stories.inspect %>

and the output was too long, so i changed it to

<%= #h @stories.inspect %>

<% @stories.each do |s| %>   <%= h s.inspect %> <% end %>

(commenting out the first line). now the code will fail to compile... saying

compile error /Users/winterheat/ror/shov2/app/views/stories/index.html.erb:13: syntax error, unexpected kENSURE, expecting ')' /Users/winterheat/ror/shov2/app/views/stories/index.html.erb:15: syntax error, unexpected kEND, expecting ')'

and if i remove that commented line altogether, the code will work. i thought in some book, it is said that you can comment out some code in ERB like that?

Update: funny if i change it to

<% #h @stories.inspect %>

then it will compile fine... so the displaying of result tag <%= %> doesn't like comments, it seems.

2

I believe that a comment in erb has to start <%# Other similar sequences have worked in some versions, or may sometimes work but are not guaranteed.

Colin

3

I've run into the same problem several times before and never thought too much of it, just made the correct change to be able to compile and kept going. Now that I think about it I might have an answer.

The ruby code is just what it is between <% and %>. Those 'delimiters' are just to tell the engine something like 'ruby code coming'. The = sign is probably actually a method call equivalent to 'puts' (I might have read that somewhere in the AWDWR book). The rest of the line is the parameter to the method. By putting the # sign after the = sign we are actually commenting out the parameter to the method but leaving the method call in place. The interpreter might not know what to do with a method call with no parameter (maybe a parameter is mandatory for the = sign method?) and burps. However if you put the # sign in front of the method call (the = sign) you are commenting the whole ruby code, hence the interpreter has no problem with it.

This is just a guess about what might be going on and if anybody knows the right answer out there I would like to know.

Pepe

4

pepe wrote:

I've run into the same problem several times before and never thought too much of it, just made the correct change to be able to compile and kept going. Now that I think about it I might have an answer.

The ruby code is just what it is between <% and %>. Those 'delimiters' are just to tell the engine something like 'ruby code coming'. The = sign is probably actually a method call equivalent to 'puts' (I might have read that somewhere in the AWDWR book). The rest of the line is the parameter to the method. By putting the # sign after the = sign we are actually commenting out the parameter to the method but leaving the method call in place. The interpreter might not know what to do with a method call with no parameter (maybe a parameter is mandatory for the = sign method?) and burps. However if you put the # sign in front of the method call (the = sign) you are commenting the whole ruby code, hence the interpreter has no problem with it.

yeah i am suspecting it is either:

<%= whatever %>

changed to <% concat(whatever) %> or changed to <% output_buffer << whatever %>

so if it is

<%= #comment %>

it becomes

<% concat( #comment ) %>

or

<% output_buffer << #comment %>

the first one fails because it comments out the ")" as well. the second one fails because it is missing something for the "<<" operator.