Geplaatst door Michiel de Mare vr, 12 dec 2008 11:23:00 GMT
Clojure is a new functional programming language based on Lisp, running on the JVM. Even though Clojure is only a year old, there’s already a book being written about it.
Since this is a Ruby site, and Rails is still the best framework for web-apps regardless of language, I’ll demonstrate how to call Clojure functions from a JRuby Rails-app.
Lees verder...Geplaatst door Michiel de Mare wo, 05 maa 2008 13:43:00 GMT
Our stock of cool tricks is depleted, but inspiration still strikes once in a while.
Are you using strftime a lot? Do you like writing strfime? Have you ever spelled it as strtime? strf_time? Thought it was frmtstr?
And if you spell it right, you still have to type those stupid %-signs. All in all, room for improvement.
class Time
def method_missing(name,*args)
if name.to_s =~ /f_/
c = args[0] || ' '
x = name.to_s[2..-1].split(//).
map {|f| f =~ /[a-z]/i ? "%"+f : c}.
join
strftime(x)
else
super
end
end
end
So, how does it work?
It handles every method starting with f_. What follows are the characters used within strftime: Y for 4-digit year, d for day of month, etc. Underscores are converted to spaces, or to the first argument, if you provide one.
Examples:
# standard lib
Time.now.strftime("%Y%j") #=> "2008065"
Time.now.strftime("s") #=> "1204725800"
Time.now.strftime("%d %m %Y") #=> "05 03 2008"
Time.now.strftime("%d-%m-%Y") #=> "05-03-2008"
Time.now.strftime("%d %b %Y") #=> "05 Mar 2008"
# new and improved
Time.now.f_Yj #=> "2008065"
Time.now.f_s #=> "1204725800"
Time.now.f_d_m_Y #=> "05 03 2008"
Time.now.f_d_m_Y('-') #=> "05-03-2008"
Time.now.f_d_b_Y #=> "05 Mar 2008"
Cool? Stupid? Why don’t you play with it ?
Geplaatst door Michiel de Mare wo, 05 maa 2008 06:24:00 GMT
What a sudden interest in avoiding NoMethodErrors on nil lately! I’ve just thought of another method. (Remember, you can solve any problem by adding a layer of indirection.)
Say you have Remco’s canonical example: person.name.upcase
Both person and person.name may be nil. So we usually write: person && person.name && person.name.upcase.
rrss? I’ve introduced
it last month. It stands for “returns result, same self”. Its definition is beyond trivial:
class Object
def rrss
yield self
end
end
rrss we can rewrite the original as:
person.rrss {|p| p.name}.rrss {|n| n.upcase}
Or with to_proc notation:
person.rrss(&:name).rrss(&:upcase).
We still need to check for nil though:
person.rrss {|p| p && p.name}.
rrss {|n| n && n.upcase}
Doesn’t this last bit look like it’s in need of a bit of refactoring? Its lack of DRY-ness jumps right out of the page.
Lees verder...Geplaatst door Remco van 't Veer vr, 29 feb 2008 07:40:00 GMT
Warning: only apply the following under parental guidance!
We know the whiny nil, as applied in Rails, but what about an obedient nil:
class NilClass
def method_missing(*args)
nil
end
end
No more monkeying like:
person && person.name && person.name.upcase
Not DRY at all! Let’s use the obedient nil instead:
person.name.upcase
This concludes our last daily method. Ode to Michiel for providing a vast amount of nice tricks!
Geplaatst door Michiel de Mare wo, 27 feb 2008 08:03:00 GMT
Do you know what I like so much about relational databases? And what I really miss in object-models? That databases make it so effortless to index data.
Imagine, you’ve got a huge pile of data, unordered, continually changing, but because your database keeps a few indexes, you can access any item you wish within a few milliseconds.
Wouldn’t it be fun if you could do that in Ruby? Especially the effortless part? It happens regularly that I’ve got an array with hundreds of items in which I have to search. That quicky gets slow, so I create a few hashes that I use as indexes. But what a difference with a real database!
Let make a first step in the right direction, and implement the make_index method.
module Enumerable
def make_index(*names)
Struct.new(*names).new(*names.map{|n| group_by(&n)})
end
end
index = User.find(:all).make_index(:login, :id, :nickname)
index.login['mdemare'] => [<#User ...>]
index.nickname['Michiel'] => [<#User ...>]
I admit, not a huge improvement yet. But we’re getting there. For another time, indexes on more than one attribute, unique indexes and indexing attributes with a natural order. (index.created_at > Time.now.at_midnight)
Geplaatst door Michiel de Mare di, 26 feb 2008 08:00:00 GMT
Searching in arrays is pretty slow. Better use a hash.
But if the array is already sorted, you can use a binary search, which works by dividing the array in two and searching in the left orthe right part, until there’s only one element left.
class Array
def bsearch(k)
x,y = -1,size
while y != x + 1 do
m = (x + y) / 2
if self[m] <= k
x = m
else
y = m
end
end
x >= 0 && self[x] == k && x
end
end
Geplaatst door Michiel de Mare di, 26 feb 2008 00:42:00 GMT
Staring at the following code, I got an idea (inspired by Arc):
specialism_codes.map {|code| SPECIALISMS[code] }Why do I have to create a block to map from a list of codes to a list of descriptions, when those codes and descriptions are all contained in a constant? Isn’t that what a Hash is, a mapping from a domain to a range? Isn’t that exactly the definition of a function in mathematics? Why then that block?
Anyway, I solved that pretty quickly:
class Hash
def to_proc
lambda {|x| self[x] }
end
end
specialism_codes.map &SPECIALISMSGeplaatst door Michiel de Mare ma, 25 feb 2008 08:00:00 GMT
Not in any way invented by us, but still extremely useful and not a part of the standard library: the Levenshtein Distance
What does it calculate? The number of characters to add, delete or switch to turn the first string into the second. Ideal for detecting typos.
# example:
levenshtein('levenstine', 'levenshtein') # => 3
# In the old days:
User.find(:all,
:conditions => ['name like ?', params[:name] + '%']])
# Now:
User.find(:all).
sort_by {|u| levenshtein(params[:name], u.name)}.
first
def levenshtein(s1, s2)
d = {}
(0..s1.size).each { |row| d[[row, 0]] = row }
(0..s2.size).each { |col| d[[0, col]] = col }
(1..s1.size).each do |i|
(1..s2.size).each do |j|
i1,j1 = i-1,j-1
cost = s1[i1] != s2[j1] ? 1 : 0
d[[i, j]] = [d[[i1, j1]] + cost,
d[[i1, j]] + 1,
d[[i, j1]] + 1].min
if i1*j1 > 0 and s1[i1] == s2[j-2] and s1[i-2] == s2[j1]
d[[i, j]] = [d[[i,j]] , d[[i-2, j-2]] + cost].min
end
end
end
d[[s1.size, s2.size]]
end
Geplaatst door Remco van 't Veer za, 23 feb 2008 11:21:00 GMT
Module View Controller is a nice concept but sometimes you need te be very creative to fit a problem in that mold. In such cases a more lowlevel approach can be much more effective. The case in ran into recently involves streaming audio from a Rails application. I wanted to recode and stream MP3 files over HTTP. There’s not much MVC about that, there’s nothing to view!
A memory refresher; what is Mongrel? Mongrel is a web server (mostly) written in Ruby. Ruby version 1.8 comes with a web server named WEBrick but its performance is very limited and not useable for public production web applications. Mongrel, on the other hand, is more like a hybrid between a greyhound and a poodle, fast and tough. The little beast is multi-threaded and can easily handle hundreds of concurrent requests.
Lees verder...Geplaatst door Remco van 't Veer vr, 22 feb 2008 08:00:00 GMT
Time travel can be very convenient but unfortunately it isn’t very easy. Reality won’t allow it but we can bend the Time class!
class Time
def self.now_with_warping
@warptime || now_without_warping
end
class << self
alias_method :now_without_warping, :now
alias_method :now, :now_with_warping
end
def warp
self.class.instance_variable_set('@warptime', self)
yield
ensure
self.class.instance_variable_set('@warptime', nil)
end
end
Time.at(0).warp do
puts "The current time is: #{Time.now}"
end
Time.at(2 ** 31 - 1).warp do
Time.now + 1
end
What’s the use? It makes testing time dependent code very easy!