Difference between -%> and %> in rails [duplicate]

问题:

This question already has an answer here:

• What is the difference between in ERB in Rails? 5 answers

I have started some rails tutorials and noticed that some of the view code blocks are like

and other code blocks are like

What is the difference between -%> and %>

If you know of some good syntax references you can point me to, that would also be helpful.

回答1:

The extra dash makes ERB not output the newline after the closing tag. There's no difference in your example, but if you have something like this:

      Hi    
 

It'll produce:

   Hi 
 

and not this:

    Hi  
 

回答2:

I'm pretty sure - before %> is no longer necessary, and should be left out.

At least in Chrome, the generated html looks the same using -%> or %>.

回答3:

If you use HAML rather than ERB you can do something similar with a less than or greater symbol than after your tag.

> will remove any whitespace around your tag and will remove any whitespace within it.

.float-left

is compiled to:

   Lorem ipsum dolor sit amet 
 

And…

%left_tag %inside> %right_tag 

is compiled to:

If you're not using HAML it's definitely worth checking out.

回答4:

UPDATE: This answer was wrong, see https://stackoverflow.com/a/25626629/895245 instead.

---

In Ruby 2.1 (not necessarily with Rails), the - removes one trailing newline:

• the newline must be the first char after the >
• no spaces are removed
• only a single newline is removed
• you must pass the '-' option to use it

Examples:

require 'erb' ERB.new("\nb").result              == "a\nb"  or raise begin ERB.new("\nb").result; rescue SyntaxError ; else raise; end ERB.new("\nb"  , nil, '-').result == "a\nb"  or raise ERB.new("\nb"  , nil, '-').result == 'ab'    or raise ERB.new(" \nb" , nil, '-').result == "a \nb" or raise ERB.new("\n b" , nil, '-').result == 'a b'   or raise ERB.new("\n\nb", nil, '-').result == "a\nb"  or raise 

Doc: http://ruby-doc.org/stdlib-2.1.1/libdoc/erb/rdoc/ERB.html

Rails 4.1 documents this at http://api.rubyonrails.org/classes/ActionView/Base.html, and appears to:

• use ERB by default at: https://github.com/rails/rails/blob/fcbdac7e82725c388bf5adf56a9a9a16d4efdbe0/actionview/lib/action_view/template/handlers.rb#L10

• set - by default at: https://github.com/rails/rails/blob/fcbdac7e82725c388bf5adf56a9a9a16d4efdbe0/actionview/lib/action_view/template/handlers/erb.rb#L77

However, Rails 4.1 does remove trailing whitespaces as documented while pure ERB does not, so there may be other differences.

Also, it is not removing the leading newlines as documented: it might be a documentation bug. Opened an issue at: https://github.com/rails/rails/issues/16766

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