A little-known feature of modern Regexp engines that help when optimizing a pattern that will be matched against long strings:

An atomic group is a group that, when the regex engine exits from it, automatically throws away all backtracking positions remembered by any tokens inside the group.

When you tell rbenv to install a Ruby it does not know about, you will get an error message.

$ rbenv install 2.1.2
ruby-build: definition not found: 2.1.2

You can list all available versions with `rbenv install --list'.

If the version you're looking for is not present, first try upgrading
ruby-build. If it's still missing, open a request on the ruby-build
issue tracker: https://github.com/sstephenson/ruby-build/issues

(Fun fact: Recent versions of ruby-build will give you a more helpful error message which...

EdgeRider 0.3.0 adds support for Rails 4.1 and Ruby 2.1. It forward-ports ActiveRecord::Base.scoped to Rails 4.1.

RSpec 3.0 deprecates the :should way of writing specs for expecting things to happen.

However, if you have tests you cannot change (e.g. because they are inside a gem, spanning multiple versions of Rails and RSpec), you can explicitly allow the deprecated syntax.

Fix

Inside spec/spec_helpber.rb, set rspec-expectations’ and/or rspec-mocks’ syntax as following:

RSpec.configure do |config|
  # ...
  config.mock_with :rspec do |c|
    c.syntax = [:should, :expect]
 ...

Sometimes you're getting an ActiveSupport deprecation warning that you cannot or don't want to fix. In these cases, it might be okay to silence some specific warnings. Add this to your initializers, or require it in your tests:

silenced = [
  /Not considered a useful test/,
  /use: should(_not)? have_sent_email/,
] # list of warnings you want to silence

silenced_expr = Regexp.new(silenced.join('|'))

ActiveSupport::Deprecation.behavior = lambda do |msg, stack|
  unless msg =~ silenced_expr
    ActiveSupport::Deprecation::DEFAULT_BEHAVI...

Warnings like those below may originate from rspec or shoulda-matchers or other gems that have not updated yet to the new MiniTest API.

One

Warning: you should require 'minitest/autorun' instead.
Warning: or add 'gem "minitest"' before 'require "minitest/autorun"'
# (backtrace)

Solution: Add gem 'minitest' to your Gemfile, before any rspec gem.

Another

MiniTest::Unit::TestCase is now Minitest::Test. From /Users/makandra/.rvm/rubies/ruby-1.9.3-p484/lib/ruby/1.9.1/tes...

jQuery plugin that makes it easy to dynamically add and remove records when using ActiveRecord's nested attributes.

ActiveRecord caches results of SQL queries. If you want to discard the cached results for one model, you can call MyModel.connection.clear_query_cache.

SimpleForm is a great approach to simplifying your forms, and it comes with lots of well-defined input types. However, the :grouped_select type seems to be overly complicated for most use cases.

Example

Consider this example, from the documentation:

form.input :country_id, collection: @continents,
  as: :grouped_select, group_method: :countries

While that looks easy enough at a first glance, look closer. The example passes @continents for a country_id.\
SimpleForm actua...

MuPDF is a PDF reader that renders very quickly, yet still correctly.

It supports PDF 1.7 and all the fancy shenanigans that evince (Ubuntu's default PDF reader) fails to render properly.

On Ubuntu, MuPDF is available in the Universe sources. Simply install via APT:

sudo apt-get install mupdf

Interaction primarily happens via keyboard, but there is basic mouse support.\
See the manpage for more details on navigating.

One downside: There is no printing support, so if...

So you want your Ruby script to install missing gems instead of dying? Take this method:

def installing_missing_gems(&block)
  yield
rescue LoadError => e
  gem_name = e.message.split('--').last.strip
  install_command = 'gem install ' + gem_name
  
  # install missing gem
  puts 'Probably missing gem: ' + gem_name
  print 'Auto-install it? [yN] '
  gets.strip =~ /y/i or exit(1)
  system(install_command) or exit(1)
  
  # retry
  Gem.clear_paths
  puts 'Trying again ...'
  require gem_name
  retry
end

Use it like this:

insta...

This is a great tutorials for beginners and intermediate AngularJS developers. It covers a lot of ground, including routing and data transfer between client and server.

The information in this card is only relevant for Rails 2.3-era apps.

This note gives a quick introduction into caching methods (page caching, action caching and fragment caching) in rails and describes some specific problems and solutions.

The descriptions below are valid for Rails 2 and 3. Recently, caching with timestamp- or content-based keys has become more popular which saves you the pain of invalidating stale caches.

How to enable/disable caching

To enable or disable caching in rails you ca...

I use this to simulate the (non-existing) :last-letter CSS pseudoclass, e. g. to insert a tombstone at the end of an article:

findLastLeaf = ($container) ->
  $children = $container.children()
  if $children.length == 0
    $container
  else
    $lastChild = $children.last()
    $lastContent = $container.contents().filter(->
      # Only return nodes that are either elements or non-empty text nodes
      @nodeType == 1 || (@nodeType == 3 && _.strip(@nodeValue) != '')
    ).last()
...

Since version 34, Chromium/Chrome ignores the autocomplete="off" attribute on forms or input fields. Recent versions of other browser do the same, although implementation details vary.

This is especially problematic for admin areas because Chrome might automatically fill in a password on a "add new user" forms.

Chrome developers say this is by design as they believe it encourages users to store more complex passwords.

Recommended fix for Chrome and F...

The error unexpected 'x' after 'DESCENDANT_SELECTOR' (Nokogiri::CSS::SyntaxError) (where x may be basically any character) occurs when the Nokogiri parser receives an invalid selector like .field_with_errors # or td <strong>.

In Cucumber, the culprit will be an invalid step definition that builds an invalid selector:

# inside some step definition:
field = find_field(label)
page.send(expectation, have_css(".field_with_errors ##{field[:id]}"))

The above raises the mentioned error if field[:id] is nil, i.e. the foun...

If you parse this Yaml ...

yes: 'Totally'
no: 'Nope'

... you get this Ruby hash:

{ true: 'Totally',
  false: 'Nope' }

In order to use the strings 'yes' and 'no' as keys, you need to wrap them with quotes:

'yes': 'Totally'
'no': 'Nope'

There's actually a long list of reserved words with this behavior:

y|Y|yes|Yes|YES|n|N|no|No|NO
|true|True|TRUE|false|False|FALSE
|on|On|ON|off|Off|OFF

I'm sorry.

You are probably using Ruby 1.8.7 with a too recent versions of Rubygems.

Downgrade your Rubygems to the latest version that works with 1.8.7.

See also

• Fix Rubygems warning: Gem.source_index is deprecated, use Specification
• Fix Rubygems binary error: undefined method `activate_bin_path' for Gem:Module (NoMethodError)
• [Bundler: Gemfile.lock is corrupt & gems are missing from the DEP...

If you get this error when you try to resize an OpenStack instance:

# nova resize example 23 --poll
ERROR: Resize requires a change in size. (HTTP 400)

You need to change your flavor to have a different memory size. It's a bug in an older OpenStack version:

        # /nova/compute/api.py
        if (current_memory_mb == new_memory_mb) and flavor_id:		
            raise exception.CannotResizeToSameSize()

which got fixed 2012-09-12 ([https://git.openstack.org/cgit/openstack/nova/commit/nova/compute/api.p...

There are 3 built-in file descriptors: stdin, stdout and stderr (std=standard). (You can define your own, see the linked article.)

Basic

• 0/1/2 references stdin/stdout/stderr
• >/2> redirects stdout/stderr, where > is taken as 1>
• &1/&2 references stdout/stderr
• &> redirects stdout and stderr = everything (caution: see below)

Caution: &> is functional as of Bash 4. This seems to result in a slightly differing behaviour when redirecting output in Ru...

quiet_assets helps with disabling asset pipeline log messages in the development log. When the gem is added, asset pipeline logs are suppressed by default.

If you want to disable muting temporarily, add config.quiet_assets = false to your config/application.rb.