'寓教于乐'学Ruby
在2005年初曾经写过一篇文章叫'结识Ruby',当时的确是刚刚结识Ruby这种语言,好奇心使然,遗憾的是之后没有坚持学习下去,也就是在这一年Ruby获得了很大的发展,特别是Ruby On Rails的出现让Ruby一下成为新兴语言的代表,甚至有人预言Ruby将会成为Java的替代者成为下一代主流语言。无论如何,Ruby的日益被广大开发人员所接受是个不争的现实,就连Martin Fowler到中国讲'敏捷'时都向中国的开发人员推荐Ruby。大师都开始学习和使用Ruby了,我们还等什么呢?有空儿的时候就多学学吧。
单纯的从学习Ruby语法的角度来看,有一个交互式学习的站点很是不错-TryRuby,感觉通过TryRuby学习Ruby基础语法就像是在玩类似'仙剑奇侠传'那种RPG游戏,有Tutorial一步一步指导你'过关',而在'过关'的过程中,Ruby相关的基础就印在你的大脑中了。
这里我把在'TryRuby'的过关过程记录下来,当然Tutorial中的一些英文说明这里被我粗略翻译为中文了:
try typing some math. Like: 2 + 6
>> 2 + 6
=> 8
Ruby能识别数字和数学符号,try some other math:
>> 4 * 10
=> 40
>> 5 – 12
=> -7
>> 40 / 10
=> 4
计算机处理数学方便快捷,我们继续,我们来看看倒转你的名字,象这样"Jimmy"输入你的名字:
>> "Tony"
=> "Tony"
一个字符串是一个计算机能够处理的字符集合,引号标识字符串的首尾,如果想翻转你的名字,敲入"Jimmy".reverse
>> "Tony".reverse
=> "ynoT"
让我们看看你的名字中到底有多少个字母:"Jimmy".length
>> "Tony".length
=> 4
看这个,我们将你的名字乘以5. "Jimmy" * 5
>> "Tony" * 5
=> "TonyTonyTonyTonyTony"
我们来看看第一分钟学到了什么。
(1) Numbers and strings are Ruby's math and text objects.
(2) Methods. You've used English-language methods like reverse and symbolic methods like * (the multiplication method.)
Methods are action!
让我们做些uncomfortable的事情,尝试翻转一个数字:40.reverse
>> 40.reverse
=> NoMethodError: undefined method `reverse' for 40:Fixnum
from (irb):10
from :0
你不能翻转一个数字,翻转一个数字没有意义,Ruby抛出一条错误信息,它在告诉你数字没有reverse方法。
也许你可以先将该数字转换成字符串:40.to_s.reverse
>> 40.to_s.reverse
=> "04"
数字和字符串不同。你可以在任何object上使用method,一些methods只能用于特定的type上,但是你可以使用Ruby's "to" method在各种类型之间作转换。
to_s converts things to strings.
to_i converts things to integers (numbers.)
to_a converts things to arrays.
Arrays是什么?它们是lists,敲入:[]
>> []
=> []
那是一个空list,lists按顺序存储things,这里有一个list,彩票号码:[12, 47, 35]
>> [12, 47, 35]
=> [12, 47, 35]
找出彩票号码中的最大值:[12, 47, 35].max
>> [12, 47, 35].max
=> 47
总是重复写[12, 47, 35]这么一个大长串比较麻烦,我们将这些彩票号码放入一个’ticket’里吧,像这样:ticket = [12, 47, 35]
>> ticket = [12, 47, 35]
=> [12, 47, 35]
现在敲入ticket:
>> ticket
=> [12, 47, 35]
彩票号码被挤入一个变量ticket中,我们来给彩票号码排个序,怎么做呢:ticket.sort!
>> ticket.sort!
=> [12, 35, 47]
现在你拥有了一个已经排好序的list了,而且变量ticket被改变了。我们来看看第二分钟我们都学到了什么东西:
(1) Errors. If you try to reverse a number or do anything fishy, Ruby will skip the prompt and tell you so.
(2) Arrays are lists for storing things in order.
(3) Variables save a thing and give it a name. You used the equals sign to do this. Like: ticket = [14, 37, 18].
打印一首诗吧
>> print poem
My toast has flown from my hand
And my toast has gone to the moon.
But when I saw it on television,
Planting our flag on Halley's comet,
More still did I want to eat it.
=> nil
试试这样一个操作:poem['toast'] = 'honeydew',之后再print poem看看我们的新诗:
>> poem['toast'] = 'honeydew'
=> "honeydew"
>> print poem
My honeydew has flown from my hand
And my toast has gone to the moon.
But when I saw it on television,
Planting our flag on Halley's comet,
More still did I want to eat it.
=> nil
[]意思是"我要找…",这里我们要在poem中找'toast'并将之替换成'honeydew',这里有一个问题,如果我们将整首诗翻转会怎样呢:poem.reverse.
>> poem.reverse
=> "\n.ti tae ot tnaw I did llits eroM\n,temoc s'yellaH no galf ruo gnitnalP\n,n
oisivelet no ti was I nehw tuB\n.noom eht ot enog sah tsaot ym dnA\ndnah ym morf
nwolf sah wedyenoh yM"
可以肯定的是整首诗都被一个字母一个字母的翻转了。其实我只是想按行翻转,即最后一行变成第一行,第一行变成最后一行,而不是像现在这样翻转,试试poem.to_a.reverse.
>> poem.to_a.reverse
=> ["More still did I want to eat it.\n", "Planting our flag on Halley's comet,\
n", "But when I saw it on television,\n", "And my toast has gone to the moon.\n"
, "My honeydew has flown from my hand\n"]
发生什么了?发生两件事:你将poem转换成array了,当Ruby将字符串转换为array时,它以每一行为一个单位,这就是我们得到上面结果的原因,因为array被翻转了。我们再来看一个method吧:print poem.to_a.reverse.join
>> print poem.to_a.reverse.join
More still did I want to eat it.
Planting our flag on Halley's comet,
But when I saw it on television,
And my toast has gone to the moon.
My honeydew has flown from my hand
=> nil
join方法将已经按行翻转的list重新组合成一个字符串,当然你也可以使用to_s方法。
Review Time:
(1) Exclamations. Methods may have exclamations (and also question marks) in their name. No big deal. Try: poem.include? "my
hand"
(2) Square brackets. Target and find things. Search and replace.
(3) Chaining methods lets you get a lot more done. Break up a poem, reverse it, reassemble it: poem.to_a.reverse.join
OK,如果你准备好继续了,敲入books = {}
>> books = {}
=> {}
你已经建立起一个空的Hash表了,现在我们准备在这个Hash中建立一个book rating系统:
:splendid -> a masterpiece.
:quite_good -> enjoyed, sure, yes.
:mediocre -> equal parts great and terrible.
:quite_not_good -> notably bad.
:abyssmal -> steaming wreck.
如果你要rate一本书,你可以像这样做:books["Gravity's Rainbow"] = :splendid,将书目放入[]中,将rating放在等号后面。
>> books["Gravity's Rainbow"] = :splendid
=> :splendid
继续填充该Hash,这些级别为the ratings are: :splendid, :quite_good, :mediocre, :quite_not_good, and :abyssmal. 它们不是strings,把一个:放在一个单词的前面,你就将得到一个符号,在内存空间占用上,符号要比string少得多. 符号在内存中只存储一次,但是可以多次使用,这点string是做不到的。如果你已经输入了3、4本书了,你可以敲入books.length来得到书的个数。
>> books["Gravity's Rainbow1"] = :quite_good
=> :quite_good
>> books["Gravity's Rainbow2"] = :quite_good
=> :quite_good
>> books["Gravity's Rainbow3"] = :quite_not_good
=> :quite_not_good
>> books.length
=> 4
如果你想查找某本书的rating,只需要将书名放入[]之间:
>> books["Gravity's Rainbow"]
=> :splendid
又到总结时间了,目前你学会了:
(1) Hashes. The little dictionary with the curly pages: {}.
(2) Symbols. Tiny, efficient code words with a colon: :splendid.
我们的'寓教于乐'就到此为止了,其实TryRuby后面还有6节内容,因为篇幅太长,这里仅是抛砖引玉,剩下的大家可以自己到TryRuby去感受去学习。
© 2006, bigwhite. 版权所有.
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