Dejan Simic

Yesterday's Weather

2010-07-03T00:00:00+02:00

Pomodoro Technique Illustrated Book:

A national weather service spent a gigantic amount of money on a new forecast system. All the emerging technology was included, and it had an accuracy rate of almost 70 percent.

Then a clever person challenged the super machine with a much simpler algorithm. It was called Yesterday’s Weather, and it said, “Tomorrow will be like today.” Guess what? It had the same accuracy as the super machine.

Distinct values in Rails

2010-05-23T00:00:00+02:00

First of all don’t do this http://snipplr.com/view/21497/distinct-in-rails. I’m not even linking it since somehow that’s already ranked #5 for “rails distinct” on Google.

One way is to use :select option in ActiveRecord finder.

>> User.all(:select => 'distinct(ip)')
=> [#<User ip: "80.74.172.18">, #<User ip: "80.74.172.13">, ... ]

As you can see this will give you ActiveRecords with only that attribute initialized. Often you need to do something with those distinct values (and not just display them) so it’s more suitable to have values (instead of ActiveRecords) in an array. Use select values for that:

>> User.connection.select_values('select distinct(ip) from users')
=> ["80.74.172.18", "80.74.172.13", ... ]

10 Rails console tricks

2009-12-20T00:00:00+01:00

Invoking helper methods

>> helper.number_to_currency('123.45')

Method definition finder (irb)

>> helper.method(:truncate)
=> #<Method: ActionView::Base(ActionView::Helpers::TextHelper)#truncate>

>> "".method(:camelize)
=> #<Method: String(ActiveSupport::CoreExtensions::String::Inflections)#camelize>

Method finder (irb)

$ gem install what_methods

>> require 'what_methods'
>> "foo ".what? "foo"
"foo ".chop! == "foo"
"foo ".chop == "foo"
"foo ".strip! == "foo"
"foo ".strip == "foo"
"foo ".rstrip! == "foo"
"foo ".rstrip == "foo"
=> ["chop!", "chop", "strip!", "strip", "rstrip!", "rstrip"]

Method lookup (irb)

>> "".methods.grep(/case/).sort
=> ["camelcase", "casecmp", "downcase", "downcase!", "swapcase", "swapcase!", "titlecase", "upcase", "upcase!"]

Avoid screenfuls of objects (irb)

>> people = Person.all; nil
=> nil

Rollback database modifications on exit

$ ./script/console --sandbox

Last expression (irb)

>> Person.first
=> #<Person id: 1, first_name: "Dejan" ... >
>> _.first_name
=> "Dejan"

Reload code changes

>> reload!

Better object format (irb)

>> y User.first
--- !ruby/object:User 
attributes: 
  hashed_password: 123456789cde83xa9b86e36e4627360
  last_seen_at: 2009-12-09 13:16:44
  username: dejan
  id: "1"
  created_at: 2007-01-14 17:30:00
attributes_cache: {}

script/console logging

You need this.

>> User.cached(:first)
==> Got User:first from cache. (0.10173)
  User Load (300.1ms)   SELECT * FROM `users` LIMIT 1
==> Set User:first to cache. (0.01512)
=> #<User id: 1, username: "dejan", ... >

>> User.cached(:first)
==> Got User:first from cache. (0.00061)
=> #<User id: 1, username: "dejan", ... >

>> User.expire_cache(:first)
==> Deleted User:first from cache. (0.00059)
=> true

Accountability

2009-02-15T00:00:00+01:00

Jay Fields: “I heard once that in Great Britain’s MOD if you design software for a plane you go up in the test plane when the software is beta-tested. If all programmers were held with that level of accountability, how many do you think would still be in our field? How many would you want to collaborate with before you went up in the plane together?”

simple_captcha while developing

2008-10-29T00:00:00+01:00

Type less is my motto these days. Not just the code, but everything.

If you’re developing an app with the excellent simple_captcha plugin do your fingers a favor and monkey patch it in development.rb:

# type less. autosolve captcha while developing
ActionView::Base.module_eval do
  def simple_captcha_field(options={})
    options[:object] ?
      text_field(options[:object], :captcha, :value => simple_captcha_value(simple_captcha_key)) +
        hidden_field(options[:object], :captcha_key, {:value => options[:field_value]}) : 
      text_field_tag(:captcha, simple_captcha_value(simple_captcha_key))
  end
end

Don't escape in Strings

2008-10-26T00:00:00+02:00

So don’t do:

"#{name} said: \"Clap your hands!\""

It’s ugly and you don’t need it. Ruby has excellent support for arbitrary delimiters for string literals.

So above can be rewritten as:

%-#{@name} says: "Clap your hands!"-

… or if String contains dash:

%/#{@name} says: "Play tic-tac-toe!"/

… or if String contains dash and slash:

%Q|#{@name} says: "Try ftp://ruby-lang.org/pub/ruby/1.9/"|

… and so on. No need to escape.

Excerpt from the great book The Ruby programming Language:

“The sequence %q begins a string literal that follows single-quoted string rules, and the sequence %Q (or just %) introduces a literal that follows double-qouted string rules. The first character following q or Q is the delimiter, and the string literal continues until a matching delimiter is found. If the opening delimiter is (, [, {, or <, then the matching delimiter is ), ], }, or >. Otherwise, the closing delimiter is the same as the opening delimiter.”

Alternative join and split in Ruby

2008-07-09T00:00:00+02:00

Join

>> %w(tic tac toe) * "-" 
=> "tic-tac-toe"

Split

>> "tic-tac-toe" / "-" 
=> ["tic", "tac", "toe"]

Unfortunately, for split you’ll need this of course:

class String
  alias / :split
end

;)

Self or default if empty, DRY way

2008-03-19T00:00:00+01:00

I really appreciate following idiom in Ruby:

person.phone || "N/A"

It’s DRY. No need for conditional structures, and repeating person.phone in condition and as return value.

But lets say you don’t control your data source, and there is an empty string instead of nil when data is not available (sounds familiar?). How would you deal with that and keep things simple and DRY?

Well, basicly all you need is a String method that will return nil if string is empty, or self if it’s not empty. String object doesn’t have that kind of method, at least not that specialized. Regexp to rescue. Lets try this:

>> ""[/.+/m]
=> nil

>> "ruby"[/.+/m]
=> "ruby"

Nice. So solution for the problem above is:

person.phone[/.+/m] || "N/A"

Throw andand in game to support both nil and empty value with no cost in complexity:

person.phone.andand[/.+/m] || "N/A"

andand

2008-03-18T00:00:00+01:00

I really, really like andand. Try it and stop repeating yourself.

I mean, why would you want to write this:

entry.at('description') && entry.at('description').inner_text

when you can write this:

entry.at('description').andand.inner_text

Eleventh

2008-02-11T00:00:00+01:00

Did you know that Ruby was Matz’ eleventh take on creating a programming language? Listen. So don’t despare next time you fail, you are right on track.

I sat down and counted the other day and Ruby was eleventh language I’ve tried to write. Out of those 4 only had names, 3 of them didn’t work at all… the rest of them was just experiments. Ruby is the only one that really worked, so I guess that makes Ruby the first one, but it was one out of eleven attempts.

~ Matz

The road to wisdom? – Well, it’s plain and simple to express: Err and err and err again but less and less and less.

~ Piet Hein

Nested Ternary Operator

2008-01-20T00:00:00+01:00

I was going through some of my old Java code and found this interesting piece of code. It’s basically alternative way of creating switch structure.

  public Object getValueAt(int row, int col) {
    Person person = data.get(row);
    return 
      col==0? person.getFirstName() 
      : col==1? person.getLastName() 
      : col==2? person.getAge()            
      : col==3? person.getAddress()
      : null; 
  }

Cons:

unlike switch, there is no compile time error for duplicated cases
this is not a standard way of dealing with different values of a variable so you could leave wondering the person that will read your code

Pros:

more control over branching logic since expressions are used (switch must use constants as case values)
this is not a standard way of dealing with different values of a variable so you could be seen as hacker in the eyes of the person that will read your code ;)