javascript closures
For given content:
<div id="test0">change me</div> <div id="test1">change me</div> <div id="test2">change me</div> <div id="test3">change me</div>
The code:
for (var i = 0; i < 4; i++) { $('#test' + i).click(function(){ $(this).html(i); }); }
will print (every time any of the elements is clicked):
4 4 4 4
Here is how this could be solved with the closure:
for (var i = 0; i < 4; i++) { (function (i){ $('#test' + i).click(function(){ $(this).html(i); }); })(i); }
managing gems with rvm named gem sets
RVM (Ruby Version Manager) is a tool which lets you install and switch between multiple ruby versions. RVM has also something called Named Gem Sets. This is pretty cool because you can create many different gem sets for different types of apps. Here is how to do it (I assume you have rvm already installed if not check this out):
- go to your project folder and create new file called .rvmrc
- open .rvmrc and add rvm ruby-version@your-gem-set for example rvm ruby-1.9.1@railsgems
- close file and type: rvm gemset create your-gem-set (this will create new set)
- type gem list (you should see empty list with no gems installed)
It’s almost as you would start with a fresh system 
Clojure syntax
Making a note for myself:
(1 2 3 4) // list [1 2 3 fred] // vector {:a 1 :b 2 :c 3}, {1 "a" 2 "b"} // map key/value #{a b c} // set
dfs in ruby :)
I wrote simple dfs in ruby:
def dfs(node, value, queue) return false if node.nil? return true if node.data == value queue.push node.right unless node.right.nil? queue.push node.left unless node.left.nil? dfs(queue.pop, value, queue) end
for node:
class Node attr_accessor :left, :right, :data end
class variables, class instance variables and instance variables in ruby
This was covered multiple times already. I’ve created this little snippet to remember the difference between different types of variables in ruby:
class A @@foo = "class variable of the class A" @foo = "class instance variable of the class A" def instance_method @foo = "instance variable of the class A" end def self.class_method1 # class variables are visible to and shared by the instance and class methods @@foo end def self.class_method2 # class instance variables are visible to and shared by the class methods @foo end end p A.new.instance_method # instance variable of the class A p A.class_method1 # class variable of the class A p A.class_method2 # class instance variable of the class A class B < A @@foo = "class variable of the class B" @foo = "class instance variable of the class B" end p B.class_method1 # class variable in B # class variable in A is overwritten by one in B !!! p A.class_method1 # class variable in B p B.class_method2 # class instance variable of the class B # class instance variable in A is NOT overwritten by one in B !!! p A.class_method2 # class instance variable of the class A
anemone with hpricot
Anemone is a pretty cool DSL used for web crawling. I used it with Hpricot to get a feeling for what’s possible. Below is a simple example which crawls and scrappes data from a popular polish real estate website otodom:
require 'rubygems' require 'sanitize' require 'anemone' require 'open-uri' require 'hpricot' #otodom.pl Anemone.crawl("http://otodom.pl/index.php?mod=search&act=searchResults&qid=46911208", {:storage => Anemone::Storage.PStore("crawl1.pstore")}) do | anemone | # filter out useless pages anemone.focus_crawl do |page| page.links.delete_if do |x| (x.to_s =~ /mod=search&act=searchResults&qid=/).nil? and (x.to_s =~ /[a-zA-Z]+-id[0-9]*\.html$/).nil? end end # process details pages anemone.on_pages_like(/[a-zA-Z]+-id[0-9]*\.html$/) do | page | doc = Hpricot(page.doc) price = doc.at("//strong[@id='offerPrice']") location = doc.at("//dl[@class='stripeMe'] > dd") desc = doc.at("//div[@id='offerDesc'] > p") offer_no = doc.at("//div[@id='offerFoot'] p[@class='toLeft']/span/strong") created_at = doc.at("//div[@id='offerFoot'] p[@class='toRight']/span/strong") photos = doc.search("//div[@id='imageList']/p/a") end end
Academia vs. Business
blocks, procs and lambdas in ruby
Nice post about block, procs and lambdas in ruby by Robert Sosinski.
changing function’s context in javascript
Today I learned how to change the context of a function in javascript. When we do:
function test() { this.foo = "Hello from " + this + " context."; } test(); alert(foo); // will show "Hello from [object Window] context.";
foo will belong to the global context. In other words global object foo will be created. We can change the context to some other object by doing:
var otherContext = {}; test.call(otherContext); alert(otherContext.foo); // will show "Hello from [object Object] context."
In this case foo will belong to otherContext.
Gemcutter & Jeweler
More about gemcutter & jeweler can be found here.
Here are the steps how to publish patched gem cloned from github:
1. Append username to gem name in .gemspec or if you use jeweler open Rakefile and edit Jeweler::Tasks section save it and run:
rake gemspec
2. Build gem with:
gem build
3. Push new gem to gemcutter
gem push