Ruby 字符串，符号，数字，日期

字符串

String 与 Symbol 这两个类提供了表示文字与处理文字的功能。这两个类之间很不同。

字符串表示

一个字符串一般用一组引号包装：

"这就是一个字符串"
单引号也行：

'我也是个字符串'
使用字符插值的时候得用双引号：

puts "二加二等于 #{2 + 2}"
puts '二加二等于 #{2 + 2}'
输出的内容是：

二加二等于 4
二加二等于 #{2 + 2}
单引与双引在 escape 时的区别：

puts "Backslashes (\) have to be escaped in double quotes."
puts 'You can just type once in a single quoted string.'
puts "But whichever type of quotation mark you use..."
puts "...you have to escape its quotation symbol, such as "."
puts 'That applies to ' in single-quoted strings too.'
puts 'Backslash-n just looks like n between single quotes.'
puts "But it means newlinenin a double-quoted string."
puts 'Same with t, which comes out as t with single quotes...'
puts "...but inserts a tab character:tinside double quotes."
puts "You can escape the backslash to get \n and \t with double quotes."
输出的是：

Backslashes () have to be escaped in double quotes.
You can just type once in a single quoted string.
But whichever type of quotation mark you use...
...you have to escape its quotation symbol, such as ".
That applies to ' in single-quoted strings too.
Backslash-n just looks like n between single quotes.
But it means newline
in a double-quoted string.
Same with t, which comes out as t with single quotes...
...but inserts a tab character: inside double quotes.
You can escape the backslash to get n and t with double quotes.
下午6:59 **

下午7:24 **

其它的引用机制

还有一种引用机制，%char{text}，下面的 %q 生成一个单引号字符：

puts %q{You needn't escape apostrophes when using %q.}
因为上面的字符串不是用单引号标记的，所以字符串里的撇号不用 escape 。

双引号用 %Q，%{} 也可以。分隔符也可以很随便：

%q-A string-
%Q/Another string/
%[Yet another string]
Here 文档

here-doc，可以是多行字符串：

>> text = This is the first line of text.
This is the second line.
Now we're done.
EOM
=> "This is the first line of text.nThis is the second line.nNow we're done.n"

>> text = The EOM doesn't have to be flush left!
EOM
=> "The EOM doesn't have to be flush left!n"
默认 here-docs 跟双引号字符串一样，可以解释它里面的字符插值，还有一些 escape 字符，比如 n 或 t 。如果你需要让 here-doc 像单引号字符串那样，可以这样：

>> text = Single-quoted!
Note the literal n.
And the literal #{2+2}.
EOM
=> "Single-quoted!nNote the literal \n.nAnd the literal #{2+2}.n"
>> puts text
Single-quoted!
Note the literal n.
And the literal #{2+2}.
=> nil
这样再试试：

>> a = 5
EOM
=> 50
再这样试一下：

>> array = [1,2,3, This is the here-doc.
It becomes array[3]
EOM
=> [1, 2, 3, "This is the here-doc.nIt becomes array[3]n", 4]
作为方法参数：

do_something_with_args(a, b, http://*so*me_ver*y_long_url_or_other_text_best_put_on_its_own_line
EOM
字符串处理

获取与设置子字符串

[] 操作符可以得到一个字符串里的某个位置上的字符。提供一个索引号就行了，索引号是从零开始的，负数的索引指的是从字符串的最后往前数。

试一下：

>> string = 'Ruby is a cool language.'
=> "Ruby is a cool language."
>> string[5]
=> "i"
>> string[-12]
=> "o"
截取一段，再给 [] 提供一个 m 参数：

>> string[5,10]
=> "is a cool "
也可以用一个 range 对象作为参数：

>> string[7..14]
=> " a cool "
>> string[-12..-3]
=> "ol languag"
>> string[-12..20]
=> "ol langua"
>> string[15..-1]
=> "language."
也可以直接给出你想得到的子字符串的内容，如果找到了就返回这个字符串，没找到就返回 nil：

>> string['cool lang']
=> "cool lang"
>> string['very cool lang']
=> nil
正则表达式：

>> string[/c[ol ]+/]
=> "cool l"
slice 与 slice!：

>> string.slice!('cool')
=> "cool"
>> string
=> "Ruby is a language."
[]= 方法可以设置找到的字符串：

>> string = 'Ruby is a cool language.'
=> "Ruby is a cool language."
>> string['cool'] = 'great'
=> "great"
>> string
=> "Ruby is a great language."
>> string[-1] = '!'
=> "!"
>> string
=> "Ruby is a great language!"
>> string[-9..-1] = 'thing to learn'
=> "thing to learn"
>> string
=> "Ruby is a great thing to learn"
合并字符串

>> 'a' + 'b'
=> "ab"
>> 'a' + 'b' + 'c'
=> "abc"
+ 得到的永远都会是一个新的字符串，这样再试一下：

>> str = 'hi '
=> "hi "
>> str + 'there.'
=> "hi there."
>> str
=> "hi "
再试试

>> str = 'hi '
=> "hi "
>> str => "hi there."
>> str
=> "hi there."
通过插值合并字符串

>> str = 'hi'
=> "hi"
>> "#{str} there."
=> "hi there."
插值里可以是任何 Ruby 表达式：

>> "the sum is #{2+2}"
=> "the sum is 4"
不信再试试这个：

>> "My name is #{
>> class Person
>> attr_accessor :name
>> end
>> d = Person.new
>> d.name = 'David'
>> d.name
>> }."
=> "My name is David."
更好的方法：Ruby 在插值里会调用对象的 to_s 方法，你可以定义自己的 to_s 方法：

>> class Person
>> attr_accessor :name
>> def to_s
>> name
>> end
>> end
=> :to_s
>> david = Person.new
=> #<0x007fbde8a195c0>