Di Wen ifyouseewendy

How to check N is a power of 2 ?

def is_a_power_of_2?(n)
  puts "#{n} is a power of 2!" if n.bit_length != (n-1).bit_length
end

from Binary and Bitwise Operations in Ruby by CooperPress http://goo.gl/4uQY7f

Bitwise

Representation

How to represent base 2, 8, 10, 16 in Integer?

There is a weird situation I haven't noticed before:

class Counter
  attr_accessor :processed, :processed_names

  def initialize
    @processed = 0
    @processed_names = []
 end

csrf.js

var csrftk = $("meta[name='csrf-token']").attr("content");

// Ajax set
$(document).ajaxSend(function(e, xhr, options) {
  xhr.setRequestHeader("X-CSRF-Token", csrftk);
});

from http://blog.honeybadger.io/advanced-ruby-hash-techniques/

Strict fetching

h = Hash.new { |hash, key| raise ArgumentError.new("No hash key: #{ key }") }
h[:a]=1
h[:a] # 1
h[:x] # raises ArgumentError: No hash key: x

`?:` - Non capture the group

http://stackoverflow.com/questions/3512471/non-capturing-group

str = "http://stackoverflow.com/questions/tagged/regex"
str =~ /(http|ftp):\/\/([^\/\r\n]+)(\/[^\r\n]*)?/
puts $1 # => http

# with ?:

	# SPOJ - PRIME1 http://www.spoj.com/problems/PRIME1/
	#
	# NOTE
	#
	# 1. Presieve the primes under sqrt(1_000_000_000).
	# 2. Multiple the primes to flag numbers which are not primes.
	# 3. Sieve in given range.

	primes = [2]

	HOST = ""
	APP_KEY = ""
	APP_SECRET = ""

	REQUEST_TOKEN = ""
	REQUEST_TOKEN_SECRET = ""
	REQUEST_TOKEN_VERIFIER = ""

	ACCESS_TOKEN = ""
	ACCESS_TOKEN_SECRET = ""

	git filter-branch -f --commit-filter '
	if [ "$GIT_COMMITTER_NAME" = "<Old name>" ];
	then
	GIT_COMMITTER_NAME="<New name>";
	GIT_COMMITTER_EMAIL="<New email>";
	GIT_AUTHOR_NAME="<New name>";
	GIT_AUTHOR_EMAIL="<New email>";
	else
	git commit-tree "$@";
	fi' -- --all

	# API
	#
	# + push
	# + top
	# + pop
	# + empty
	# + empty?

	ArrayStack = Struct.new(:values) do
	def push(value)

Di Wen ifyouseewendy

Bitwise

Representation

Strict fetching

?: - Non capture the group

`?:` - Non capture the group