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Ruby: Dicas & Truques
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Nando Vieira
July 07, 2012
Technology
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Ruby: Dicas & Truques
Nando Vieira
July 07, 2012
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Transcript
DICAS & TRUQUES RUBY Nando Vieira hellobits.com
@fnando
None
None
None
DICAS E TRUQUES CURIOSOS QUE PODEM SER ÚTEIS (OU NÃO)
NO DIA-A-DIA.
None
No Ruby, tudo é objeto (ou quase tudo).
Classes, módulos, números, strings, arrays, intervalos, símbolos, métodos, blocos, procs,
nil, booleanos, hashes, expressões regulares.
O Ruby possui classes abertas que podem ser modi cadas
a qualquer momento.
O Ruby é extremamente exível.
O Ruby é muito mais difícil do que as pessoas
assumem.
DUCK TYPING, PROTOCOLOS E CONTRATOS
O Duck Typing permite estabelecer interfaces com um contrato informal.
class SimpleLogger def initialize(storage = []) unless storage.is_a?(Array) raise "you
need to pass an array" end @storage = storage end def log(message) @storage << message end end
def initialize(storage = []) unless storage.is_a?(Array) raise "you need to
pass an array" end @storage = storage end
def log(message) @storage << message end
@storage.<<(value)
File#<< String#<< Array#<< CSV#<< Set#<< IO#<< StringIO#<< Queue#<<
class SimpleLogger def initialize(storage = []) @storage = storage end
def log(message) @storage << message end end
logger = SimpleLogger.new(nil) logger.log("Hello") #=> NoMethodError: undefined #=> method `<<'
for nil:NilClass
O Ruby leva o Duck Typing por toda a linguagem,
usando-o como protocolo de coersão.
#to_a #to_ary #to_d #to_f #to_i #to_proc #to_s
#to_proc
people = Person.all names = people.map do |person| person.name end
people = Person.all names = people.map(&:name)
&Na assinatura do método, converte bloco em Proc.
&Na chamada do método, converte Proc em bloco.
method(&object)
object.to_proc
people.map(&:name)
:name.to_proc #=> #<Proc:0x871cd04>
:name .to_proc .call(people.first)
class Symbol def to_proc proc do |target| target.public_send(self) end end
end
PROCS & LAMBDAS
sum_proc = proc do |n1, n2| n1 + n2 end
sum_lambda = lambda do |n1, n2| n1 + n2 end
sum_proc.class #=> Proc sum_lambda.class #=> Proc
sum_proc.lambda? #=> false sum_lambda.lambda? #=> true
sum_proc.parameters #=> [[:opt, :n1], [:opt, :n2]] sum_lambda.parameters #=> [[:req, :n1],
[:req, :n2]]
Os parâmetros de um lambda são obrigatórios por padrão.
sum_proc.call #=> NoMethodError: undefined #=> method `+' for nil:NilClass sum_lambda.call
#=> ArgumentError: wrong number #=> of arguments (0 for 2)
def proc_return proc { return "returning from proc" }.call "proc
has finished" end puts proc_return #=> returning from proc
O retorno da proc, na verdade, faz com que o
método pare de executar.
def lambda_return lambda { return "lambda: exiting method" }.call "lambda
has finished" end puts lambda_return #=> lambda has finished
O retorno do lambda é auto- contido e não afeta
o método.
O retorno de procs pode, inclusive, lançar exceções.
lambda { return "hello" }.call #=> hello proc { return
"hello" }.call #=> LocalJumpError: unexpected return
proc { next "hello" this_wont_be_executed }.call
CALLABLE OBJECTS
hello = proc do |name| puts "hello, #{name}!" end
hello.call("John")
hello["John"]
hello.("John")
hello === "John"
object = 9 multiple_of_3 = proc do |n| n.modulo(3).zero? end
case object when multiple_of_3 "is multiple of 3" when Array
"is a array" when /@/ "contains at-sign" else "couldn't understand" end
Proc#=== Regexp#=== Module#===
Array === [] #=> true multiple_of_3 === 9 #=> true
/@/ === "
[email protected]
" #=> true
Object#method Module#instance_method
Métodos não são objetos de primeira classe.
Estendendo métodos sem ter que criar uma nova classe.
class Hellobits def cool # do something end end
class Hellobits alias_method :original_cool, :cool def cool # do something
before original_cool # do something after end end
class Hellobits cool_method = instance_method(:cool) define_method :cool do # do
something before cool_method.bind(self).call # do something after end end
SPLATTING
*args
class Module def attr_dsl(*args) args.each do |arg| # do something
end end end
class Settings names = %w[path size locale] attr_dsl *names end
def coords(*) # do something -23.598737, -46.674685 end latitude, longitude
= coords
a, b, c, d = [1, 2, 3, 4]
a, b, c, d = 1, 2, 3, 4
a, b, *c = 1, 2, 3, 4 #=> a=1,
b=2, c=[3,4]
a, *b, c = 1, 2, 3, 4 #=> a=1,
b=[2,3], c=4
numbers = [1, 2, 3] more_numbers = [*numbers, 4, 5,
6] #=> [1, 2, 3, 4, 5, 6]
(1..10).to_a.sample [*1..10].sample
date = "2012-07-10" regex = /(\d+)-(\d+)-(\d+)/ _, year, month, day
= *date.match(regex)
class Sample def to_a [1, 2, 3] end end a,
b, c = *Sample.new
MAIS SOBRE ATRIBUIÇÕES
path = nil if !path path = "/some/default/path" end
path = nil path = "/some/path" unless path
path = nil path ||= "/some/path"
variable || variable = expr
html = nil if html html << "<p>Hello</p>" end
html = nil html << "<p>Hello</p>" if html
html = nil html &&= html << "<p>Hello</p>"
variable && variable = expr
DE ONDE VEM ESSE MÉTODO
user = User.new user.methods #=> [:name, :age, ...]
user.method(:name)
Method#arity Method#name Method#owner Method#parameters Method#source_location
user.method(:name) .source_location #=> ["/tmp/user.rb", 2]
EXPRESSÕES REGULARES
person = "John <
[email protected]
>" regex = /(.*?) <(.*?)>/ _, name,
email = *person.match(regex)
person[/(.*?) <(.*?)>/, 1] person[/(.*?) <(.*?)>/, 2]
person .match(/(?<name>.*?) <(?<email>.*?)>/)
match.names #=> ["name", "email"] match.captures #=> ["John Doe", "
[email protected]
"] match[:name]
#=> "John Doe" match[:email] #=> "
[email protected]
"
ENUMERATORS
names.each(&block) names.each_with_index(&block)
names.each_with_index do |name, index| puts "#{index + 10}. #{name}" end
names .each .with_index(10) do |name, index| puts "#{index}. #{name}" end
names .sort .uniq .each .with_index(10, &block)
HASHES & ENUMERATORS
hash.each do |key, value| # do something end
hash .each .with_index(10) do |pair, index| name, value = pair
# do something end
hash .each .with_index(10) do |(name, value), index| # do something
end
SYMBOLS
:name
:"full name"
:"hello #{name}"
E PARA FINALIZAR...
O Ruby possui uma série de truques que podem ajudar
bastante.
Mais do que saber usar, você precisa saber quando usar.
Sintaxes exotéricas serão mais difíceis de entender.
Conheça Ruby. Todo o resto vem de graça.
OBRIGADO!