基础

从命令行执行Ruby

通过irb启动Ruby的交互式命令行。

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>> puts 'hello, world'
hello, world
=> nil
>> language = 'Ruby'
=> "Ruby"
>> puts "hello. #{language}"
hello, Ruby
=> nil
>> language = 'my Ruby'
=> "my Ruby"
>> puts "hello, #{language}"
hello, Ruby
=> nil

一切都是对象

Ruby是一门纯面向对象语言。在本章中你将看到,Ruby是如何深入挖掘面向对象思想的。先来看一些基本对象:

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>> 4
=> 4
>> 4.class
=> Fixnum < Integer
>> 4 + 4
=> 8
>> 8
=> 8
>> 4.methods
=> [
    [  0]                               !()                 Fixnum (BasicObject)
    [  1]                              !=(arg1)             Fixnum (BasicObject)
    [  2]                              !~(arg1)             Fixnum (Kernel)
    [  3]                               %(arg1)             Fixnum
    [  4]                               &(arg1)             Fixnum
    [  5]                               *(arg1)             Fixnum
    [  6]                              **(arg1)             Fixnum
    [  7]                               +(arg1)             Fixnum
    [  8]                              +@()                 Fixnum (Numeric)
    [  9]                               -(arg1)             Fixnum
    [ 10]                              -@()                 Fixnum
    [ 11]                               /(arg1)             Fixnum
    ...

true 和 false

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>> puts 'This appears to be true.'
This appears to be true.
=> nil
>> puts 'This appears to be true.' if 'random string'
(pry):21: warning: string literal in condition
This appears to be true.
=> nil
>> puts 'This appears to be true.' if 0
This appears to be true.
=> nil
>> puts 'This appears to be true.' if true
This appears to be true.
=> nil
>> puts 'This appears to be true.' if false
=> nil
>> puts 'This appears to be true.' if nil
=> nil
>>

也就是说，除了nil和false之外，其他值都代表true。C和C++程序员可得小心了,0也是true!

逻辑运算符

Ruby的逻辑运算符,跟C、C++、C#、Java差不多,但也稍有不同。

  • and(也可写为&&)是逻辑与，or(也可写为||)是逻辑或。这两种运算符为短路求值运算符：即用这两种运算符验证表达式时,一旦表达式的值已能明确求出,解释器就不再继续执行后面的表达式代码1
  • 如果想执行整个表达式的话,可以用&或|进行比较。

下面,看看它们是如何运行的:

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>> true and false
=> false
>> true or false
=> true
>> false && false
=> false
>> true && this_will_cause_an_error
NameError: undefined local variable or method `this_will_cause_an_error' for #<IRB::TopLevel:0x00000003ae4838>
from (pry):29:in `__pry__'
>> false && this_will_not_cause_an_error
=> false
>> true || this_will_not_cause_an_error
=> true
>> true or this_will_not_cause_an_error
=> true
>> false || this_will_cause_an_error
NameError: undefined local variable or method `this_will_cause_an_error' for #<IRB::TopLevel:0x00000003ae4838>
from (pry):32:in `__pry__'
>> true | false
=> true

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