In ruby one can freeze all constant strings in a file via two different magic comments at the beginning of a file:
# frozen_string_literal: true
and
# -*- immutable: string -*-
I have no idea what the differences are.
Are there any?
The 1st syntax is the magic comment for Ruby 2.3+ versions to freeze string literals, otherwise you have to use the String method like this:
'hello world!'.freeze
The 2nd syntax is not implemented in Ruby, however it is the way that variables are specified for files in the Emacs text editor.
For example, the following comment in Emacs would declare that the file is a Ruby file and needs Ruby syntax highlighting, and that the variable immutable is set to the value string.
# -*- mode: ruby; immutable: string -*-
After searching around, it looks like that does nothing and is not used by any Ruby syntax highlighting mode.
So you do not need the 2nd syntax.
Digging for anything on the 2nd version, it looks like they had the same intention but the 2nd magic comment syntax does not to appear to have been adopted as of Ruby 2.1.0.
See https://github.com/ruby/ruby/pull/487
The first version # frozen_string_literal: true was adopted in Ruby 2.3.0
I tried the latter version in a few versions of ruby but didn't work. I would guess it should not be used or trusted to work in any version of >= 2.3 but probably no versions support it. In fact, I was not able to find any reference to that version in the open source code on github searching that syntax
https://github.com/ruby/ruby/search?q=immutable%3A+string&unscoped_q=immutable%3A+string
Related
I can't seem to find the right combination of String#encode shenanigans.
I think I'd got confused on this one so I'll post this here to hopefully help anyone else who is similarly confused.
I was trying to do my encoding in an irb session, which gives you
irb(main):002:0> 'I’d'.force_encoding('UTF-8')
=> "I’d"
And if you try using encode instead of force_encoding then you get
irb(main):001:0> 'I’d'.encode('UTF-8')
=> "I’d"
This is with irb set to use an output and input encoding of UTF-8. In my case to convert that string the way I want it involves telling Ruby that the source string is in windows-1252 encoding. You can do this by using the -E argument in which you specify `inputencoding:outputencoding' and then you get this
$ irb -EWindows-1252:UTF-8
irb(main):001:0> 'I’d'
=> "I\xC3\xA2\xE2\x82\xAC\xE2\x84\xA2d"
That looks wrong unless you pipe it out, which gives this
$ ruby -E Windows-1252:UTF-8 -e "puts 'I’d'"
I’d
Hurrah. I'm not sure about why Ruby showed it as "I\xC3\xA2\xE2\x82\xAC\xE2\x84\xA2d" (something to do with the code page of the terminal?) so if anyone can comment with further insight that would be great.
I expect your script is using the encoding cp1251 and you have ruby >= 1.9.
Then you can use force_encoding:
#encoding: cp1251
#works also with encoding: binary
source = 'I’d'
puts source.force_encoding('utf-8') #-> I’d
If my exceptions are wrong: Which encoding do you use and which ruby version?
A little background:
Problems with encoding are difficult to analyse. There may be conflicts between:
Encoding of the source code (That's defined by the editor).
Expected encoding of the source code (that's defined with #encoding on the first line). This is used by ruby.
Encoding of the string (see e.g. section String encodings in http://nuclearsquid.com/writings/ruby-1-9-encodings/ )
Encoding of the output shell
I am trying to run the ruby script found here
but I am getting the error
invalid multibyte char (US-ASCII)
for line 12 which is
http = Net::HTTP.new("twitter.com", Net::HTTP.https_default_port())
can someone please explain to me what this means and how I can fix it, thanks
When you run the script with Ruby 1.9, change the first two lines of the script to:
#!/usr/bin/env ruby
# encoding: utf-8
require 'net/http'
This tells Ruby to run the script with support for the UTF-8 character set. Without that line Ruby 1.9 would default to the US_ASCII character set.
Just for the record: This will not work in Ruby 1.8, because 1.8 doesn't knew anything about string encodings. And the line is not needed anymore in Ruby 2.0, because Ruby 2.0 is using UTF-8 as the default anyway.
It means that a multibyte character is used and Ruby is not set to handle it. If you are using an old version of Ruby, then put the following magic comment at the beginning of the file:
# coding: utf-8
If you use a modern version of Ruby, then that problem would not arise in the first place.
How does the magic comment in ruby works? I am talking about:
# Encoding: utf-8
Is this a preprocessing directive? Are there other uses of this type of construction?
Ruby interpreter instructions at the top of the source file - this is called magic comment. Before processing your source code interpreter reads this line and sets proper encoding. It's quite common for interpreted languages I believe. At least Python uses the same approach.
You can specify encoding in a number of different ways (some of them are recognized by editors):
# encoding: UTF-8
# coding: UTF-8
# -*- coding: UTF-8 -*-
You can read some interesting stuff about source encoding in this article.
The only thing I'm aware of that has similar construction is shebang, but it is related to Unix shells in general and is not Ruby-specific.
magic_comments defined in ruby/ruby
This magic comment tells Ruby the source encoding of the currently parsed file. As Ruby 1.9.x by default assumes US_ASCII you have tell the interpreter what encoding your source code is in if you use non-ASCII characters (like umlauts or accented characters).
The comment has to be the first line of the file (or below the shebang if used) to be recognized.
There are other encoding settings. See this question for more information.
Since version 2.0, Ruby assumes UTF-8 encoding of the source file by default. As such, this magic encoding comment has become a rarer sight in the wild if you write your source code in UTF-8 anyway.
As you noted, magic comments are a special preprocessing construct. They must be defined at the top of the file (except, if there is already a unix shebang at the top). As of Ruby 2.3 there are three kinds of magic comments:
Encoding comment: See other answers. Must always be the first magic comment. Must be ASCII compatible. Sets the source encoding, so you will run into problems if the real encoding of the file does not match the specified encoding
frozen_string_literal: true: Freezes all string literals in the current file
warn_indent: true: Activates indentation warnings for the current file
More info: Magic Instructions
While this isn't exactly an answer for your question, if you want to read more about encodings, how they work, what kinds of problems crop up with them: the great Yehuda Katz wrote about encodings as they were being worked out in Ruby 1.9 and beyond:
Ruby 1.9 Encodings: A Primer and the Solution for Rails
Encodings, Unabridged
Originally this bug was posted here: https://rails.lighthouseapp.com/projects/8994/tickets/5713-ruby-19-ku-incompatible-with-mem_cache_store
And now, as we've run into the same issue, I'll copy here a question from that issue, hoping someone have an answer already:
When Ruby 1.9 is started in unicode mode (-Ku), mem_cache_store.rb fails to parse:
/usr/local/ruby19/bin/ruby -Ku /usr/local/ruby-1.9.2-p0/lib/ruby/gems/1.9.1/gems/
activesupport-3.0.0/lib/active_support/cache/mem_cache_store.rb
/usr/local/ruby-1.9.2-p0/lib/ruby/gems/1.9.1/gems/activesupport-3.0.0/lib/active_support/
cache/mem_cache_store.rb:32: invalid multibyte escape: /[\x00-\x20%\x7F-\xFF]/
Our case is practically identical: when you set config.action_controller.cache_store to :mem_cache_store, and try to run tests, console, or server, you recieve this in return:
/Users/%username%/.rvm/gems/ruby-1.9.2-p0/gems/activesupport-3.0.1/lib/active_support/
cache/mem_cache_store.rb:32: invalid multibyte escape: /[\x00-\x20%\x7F-\xFF]/
Any ideas how this can be avoided?..
Ruby 1.9 in unicode mode will attempt to interpret the regular expression as unicode. To avoid this you need to pass the regular expression option "n" for "no encoding":
ESCAPE_KEY_CHARS = /[\x00-\x20%\x7F-\xFF]/n
Now we have our raw 8-bit encoding (the only thing Ruby 1.8 speaks) as intended:
ruby-1.9.2-p136 :001 > ESCAPE_KEY_CHARS = /[\x00-\x20%\x7F-\xFF]/n.encoding
=> # <Encoding:ASCII-8BIT>
Hopefully the Rails teams fixes this, for now you have to edit the file.
I have a script running on Ruby 1.9.1 on Windows 7
I've distilled my script down to
File.open("翻譯測試.txt")
and still can't get it to work. I know there are issues with Ruby 1.9 filename handling on windows (Using the Windows ANSI library), but would be happy enough with a work around that is callable from Ruby
Most of the Unicode changes like file and directory operations have been improved in 1.9.2 (trunk) and other bigger changes will be merged pretty soon.
As bobince pointed out, this was already asked:
Unicode filenames on Windows in Ruby
This should help you
string = "翻譯測試" # by default, string is encoded as "ASCII"
string.force_encoding("SHIFT-JIS") # retags the String as SHIFT-JIS or whatever UTF char set that #is in
Heres a nice read a bit about char encoings in 1.9.1
http://yehudakatz.com/2010/05/17/encodings-unabridged/