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Ruby初探

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python和ruby的区别

python经常被拿来和ruby做比较, 他们都是动态脚本语言, 在应用场景上面也非常相似. 我们听到的, 它们之间广为认知的区别是:

python ~ “There should be one – and preferably only one – obvious way to do

it."

ruby ~ “There Is More Than One Way To Do It.”

但是远远不止这些, 它们之间有无数的细节不同. 根据ruby官方网站上面给出的 针对python程序员的介绍 :

  • Strings are mutable. 字符串是可写的.
  • You can make constants (variables whose value you don’t intend to change). 可以设置常量.
  • There are some enforced case-conventions (ex. class names start with a capital letter, variables start with a lowercase letter). 强制名称大小写.
  • There’s only one kind of list container (an Array), and it’s mutable. 只有一个list容器
  • Double-quoted strings allow escape sequences (like t) and a special “expression substitution” syntax (which allows you to insert the results of Ruby expressions directly into other strings without having to “add ” + “strings ” + “together”). Single-quoted strings are like Python’s r”raw strings”. “”字符串可以内嵌语句
  • There are no “new style” and “old style” classes. Just one kind. 只有一种类.(相对python有新旧之分)
  • You never directly access attributes. With Ruby, it’s all method calls. 无法访问类的属性, 只能通过方法访问.
  • Parentheses for method calls are usually optional. 执行方法可以不用括号.
  • There’s public, private, and protected to enforce access, instead of Python’s _voluntary_ underscore __convention__. 可以限制类方法的访问范围了.
  • “mixin’s” are used instead of multiple inheritance. mixin取代了多重继承.
  • You can add or modify the methods of built-in classes. Both languages let you open up and modify classes at any point, but Python prevents modification of built-ins — Ruby does not. 可以修改系统内建类的方法.
  • You’ve got true and false instead of True and False (and nil instead of None). true/false/nil取代True/False/None
  • When tested for truth, only false and nil evaluate to a false value. Everything else is true (including 0, 0.0, “”, and []). 只有false/nil为假, 其他都为真.
  • It’s elsif instead of elif. elsif取代elif
  • It’s require instead of import. Otherwise though, usage is the same. require取代import.
  • The usual-style comments on the line(s) above things (instead of docstrings below them) are used for generating docs. 代码上面的注释是文档.
  • There are a number of shortcuts that, although give you more to remember, you quickly learn. They tend to make Ruby fun and very productive. 很多快捷方式增加产能.
  • There’s no way to unset a variable once set (like Python’s del statement). You can reset a variable to nil, allowing the old contents to be garbage collected, but the variable will remain in the symbol table as long as it is in scope. 变量是持久的, 不能被删除(除非自动垃圾收集掉)

上面只是一个总览, 没有给出实际的写ruby的感觉. 我们还是通过示例来看看ruby的特质.

ruby特质

下面的内容取自 the ruby programming language.

首先, ruby是面向对象的. 所有的值都是对象, 比如:

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1.class   # => Fixnum
0.0.class # => Float

注意上面, 函数和方法(上面的class)可以不用带括号, 直接执行, 并且没有歧义. ruby是不能直接访问属性的, 所以不会混淆.

blocks 和 iterators 对python程序员看起来有点怪异, 但是看多了还是很好理解:

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3.times {print "ruby"}  # 打印3遍 ruby
1.upto(9) {|x| print x} # 打印 123456789

times和upto是整型的方法, 他们返回一个迭代器, 然后这个迭代器就执行下面{}内的代码.

ruby也有list和dict对应的数据结构:

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a  = [1, 2, 3, 4] # 和python一样也有list
a.map do     # do end和{}等价
    |x| x*x
end

# :one是符号, 如果你知道lisp, 应该明白这个是什么, 
# 如果你不知道.. 我也不知道怎么说, 就是符号啦.
# ruby的hash table写法好像没有python简洁.   
d = {:one => 1, :two => 2, "3" => 3}
d[:one] # => 1
d.each do |key, value|
    print "#{value} : #{key}; " # ruby 里面的字符串可以嵌入语句
end

ruby的语法是面向表达式的, if之类的控制符也是表达式, 比如:

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minimum = if x < y then x else y end

ruby的操作符是作为方法来实现的, 比如 + – * / [] 等, 都可以按照需要来定义.

取值和赋值是用不同的方法, 只是读取, 用 [], 如果要赋值, 就要用 []= 了.

这些个概念的区别, 需要好好体会.

方法定义:

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def square(x) # 没有":"
    x*x       # 方法的返回值是最后一个表达式的值.
end

赋值:

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x  = 12
x += 1
a, b = 1, 2 # 可以同时赋值多个变量

还有些值得一提的对象: 正则表达式对象(Regexp)和范围对象(Range):

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1..10 === 5         # 5在1..10中间
/\d{5}/ === "12345" # 匹配5个数字

上面的1..10是Range, /d{5}/是Regexp.

然后是类了:

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class Seq
    include Enumerate # 导入Enumerate module
    def initialize(from, to, by) # 初始化函数, 和__init__一样.
        @from, @to, @by = from, to, by # @表示的是类的属性.
    end

def each
    x = @from
    while x <= @to # while做循环
        yield x # 和python的yield一样.
        x += @by
    end
end

s = Seq.new(1, 10, 2)
s.each {|x| print x} #显示 "13579"

还有一些令人意外的东西:

ruby的字符串是可变的, 比如:

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s = "hello"
s[1..2]= "mo"
s # => "hmolo"

ruby里面, 只有false和nil是假, 0和”“都是为真, 需要注意.

如何学习ruby

直接去 `ruby看官方文档` 吧. 当然, 作者写的书: the ruby programming language 是深入了解ruby的基础, 和K&R对C的重要性一样.

结论

花了一下午的时间熟悉ruby, 学习前, 感觉ruby会很繁杂, 以及会有”有了python干嘛学习ruby”的想法. 真正开始学了之后, 还是体会到一点ruby的精妙之处的. 个人感觉ruby离lisp比较近(当然, 只有lisp才有那么强大的宏). 等我再深入一点ruby, 再看看有什么意思吧. 恩, 还有ruby的神器: ruby on rails.

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