Ruby: Dicas & Truques - Speaker Deck

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DICAS & TRUQUES RUBY Nando Vieira hellobits.com

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@fnando

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DICAS E TRUQUES CURIOSOS QUE PODEM SER ÚTEIS (OU NÃO) NO DIA-A-DIA.

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No Ruby, tudo é objeto (ou quase tudo).

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Classes, módulos, números, strings, arrays, intervalos, símbolos, métodos, blocos, procs, nil, booleanos, hashes, expressões regulares.

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O Ruby possui classes abertas que podem ser modi cadas a qualquer momento.

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O Ruby é extremamente exível.

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O Ruby é muito mais difícil do que as pessoas assumem.

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DUCK TYPING, PROTOCOLOS E CONTRATOS

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O Duck Typing permite estabelecer interfaces com um contrato informal.

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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

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def initialize(storage = []) unless storage.is_a?(Array) raise "you need to pass an array" end @storage = storage end

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def log(message) @storage << message end

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@storage.<<(value)

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File#<< String#<< Array#<< CSV#<< Set#<< IO#<< StringIO#<< Queue#<<

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class SimpleLogger def initialize(storage = []) @storage = storage end def log(message) @storage << message end end

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logger = SimpleLogger.new(nil) logger.log("Hello") #=> NoMethodError: undefined #=> method `<<' for nil:NilClass

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O Ruby leva o Duck Typing por toda a linguagem, usando-o como protocolo de coersão.

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#to_a #to_ary #to_d #to_f #to_i #to_proc #to_s

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#to_proc

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people = Person.all names = people.map do |person| person.name end

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people = Person.all names = people.map(&:name)

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&Na assinatura do método, converte bloco em Proc.

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&Na chamada do método, converte Proc em bloco.

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method(&object)

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object.to_proc

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people.map(&:name)

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:name.to_proc #=> #

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:name .to_proc .call(people.first)

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class Symbol def to_proc proc do |target| target.public_send(self) end end end

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PROCS & LAMBDAS

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sum_proc = proc do |n1, n2| n1 + n2 end sum_lambda = lambda do |n1, n2| n1 + n2 end

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sum_proc.class #=> Proc sum_lambda.class #=> Proc

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sum_proc.lambda? #=> false sum_lambda.lambda? #=> true

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sum_proc.parameters #=> [[:opt, :n1], [:opt, :n2]] sum_lambda.parameters #=> [[:req, :n1], [:req, :n2]]

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Os parâmetros de um lambda são obrigatórios por padrão.

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sum_proc.call #=> NoMethodError: undefined #=> method `+' for nil:NilClass sum_lambda.call #=> ArgumentError: wrong number #=> of arguments (0 for 2)

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def proc_return proc { return "returning from proc" }.call "proc has finished" end puts proc_return #=> returning from proc

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O retorno da proc, na verdade, faz com que o método pare de executar.

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def lambda_return lambda { return "lambda: exiting method" }.call "lambda has finished" end puts lambda_return #=> lambda has finished

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O retorno do lambda é auto- contido e não afeta o método.

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O retorno de procs pode, inclusive, lançar exceções.

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lambda { return "hello" }.call #=> hello proc { return "hello" }.call #=> LocalJumpError: unexpected return

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proc { next "hello" this_wont_be_executed }.call

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CALLABLE OBJECTS

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hello = proc do |name| puts "hello, #{name}!" end

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hello.call("John")

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hello["John"]

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hello.("John")

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hello === "John"

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object = 9 multiple_of_3 = proc do |n| n.modulo(3).zero? end

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case object when multiple_of_3 "is multiple of 3" when Array "is a array" when /@/ "contains at-sign" else "couldn't understand" end

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Proc#=== Regexp#=== Module#===

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Array === [] #=> true multiple_of_3 === 9 #=> true /@/ === "[email protected]" #=> true

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Object#method Module#instance_method

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Métodos não são objetos de primeira classe.

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Estendendo métodos sem ter que criar uma nova classe.

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class Hellobits def cool # do something end end

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class Hellobits alias_method :original_cool, :cool def cool # do something before original_cool # do something after end end

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class Hellobits cool_method = instance_method(:cool) define_method :cool do # do something before cool_method.bind(self).call # do something after end end

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SPLATTING

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*args

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class Module def attr_dsl(*args) args.each do |arg| # do something end end end

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class Settings names = %w[path size locale] attr_dsl *names end

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def coords(*) # do something -23.598737, -46.674685 end latitude, longitude = coords

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a, b, c, d = [1, 2, 3, 4]

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a, b, c, d = 1, 2, 3, 4

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a, b, *c = 1, 2, 3, 4 #=> a=1, b=2, c=[3,4]

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a, *b, c = 1, 2, 3, 4 #=> a=1, b=[2,3], c=4

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numbers = [1, 2, 3] more_numbers = [*numbers, 4, 5, 6] #=> [1, 2, 3, 4, 5, 6]

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(1..10).to_a.sample [*1..10].sample

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date = "2012-07-10" regex = /(\d+)-(\d+)-(\d+)/ _, year, month, day = *date.match(regex)

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class Sample def to_a [1, 2, 3] end end a, b, c = *Sample.new

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MAIS SOBRE ATRIBUIÇÕES

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path = nil if !path path = "/some/default/path" end

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path = nil path = "/some/path" unless path

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path = nil path ||= "/some/path"

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variable || variable = expr

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html = nil if html html << "

Hello

" end

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html = nil html << "

Hello

" if html

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html = nil html &&= html << "

Hello

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variable && variable = expr

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DE ONDE VEM ESSE MÉTODO

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user = User.new user.methods #=> [:name, :age, ...]

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user.method(:name)

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Method#arity Method#name Method#owner Method#parameters Method#source_location

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user.method(:name) .source_location #=> ["/tmp/user.rb", 2]

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EXPRESSÕES REGULARES

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person = "John " regex = /(.*?) <(.*?)>/ _, name, email = *person.match(regex)

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person[/(.*?) <(.*?)>/, 1] person[/(.*?) <(.*?)>/, 2]

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person .match(/(?.*?) <(?.*?)>/)

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match.names #=> ["name", "email"] match.captures #=> ["John Doe", "[email protected]"] match[:name] #=> "John Doe" match[:email] #=> "[email protected]"

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ENUMERATORS

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names.each(&block) names.each_with_index(&block)

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names.each_with_index do |name, index| puts "#{index + 10}. #{name}" end

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names .each .with_index(10) do |name, index| puts "#{index}. #{name}" end

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names .sort .uniq .each .with_index(10, &block)

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HASHES & ENUMERATORS

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hash.each do |key, value| # do something end

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hash .each .with_index(10) do |pair, index| name, value = pair # do something end