blocks|key|933329|text|这只是个惯例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|933330|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

blocks|key|933398|text|这两种语法之间有细微的差别。{+}比do+...+end具有更高优先级。因此，下面的代码将把bar和一个块传递给foo方法|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|933399|foo+bar+do+...+end|code-block|syntax|javascript|933400|而下面的代码会将一个块传递给bar，并将结果传递给foo|933401|foo+bar+{+...+}|933402|因此，您的示例将执行相同的操作。但是，如果您去掉了括号：|933403|>+3.upto+9+{+
++puts+"Hi"+
}
SyntaxError:+compile+error
(irb):82:+syntax+error,+unexpected+'{',+expecting+$end
3.upto+9+{+
++++++++++%5E
++++from+(irb):82
++++from+:0

>+3.upto+9+do+
++++puts+"Hi"+
++end
Hi
Hi
Hi
Hi
Hi
Hi
Hi
=>+3|933404|因此，如果您在Ruby语言中去掉括号，{+}更有可能赶上您，这是相当常见的；出于这个原因，并且由于Ruby和其他控制构造都使用end作为分隔符，人们通常将do+...+end用于语句末尾的多行代码块。|933405|但是，{+}经常用于do+...+end比较麻烦地方，例如，如果您要将接受块的几个方法链接在一起。这可以让您编写简短的、一行的小块，这些块可以用作方法链的一部分。|933406|>+[1,2,3].sort{%7Cx,y%7C+y<=>x}.map{%7Cx%7C+x%2B1}
=>+[4,+3,+2]|933407|这里有一个例子来说明这一区别：|933408|def+foo+arg
++if+block_given?
++++puts+"Block+given+to+foo"
++++yield+arg
++else
++++puts+"No+block+given+to+foo"
++++arg
++end
end


def+bar
++if+block_given?
++++puts+"Block+given+to+bar"
++++yield+"Yielded+from+bar"
++else
++++puts+"No+block+given+to+bar"
++end
++"Returned+from+bar"
end

irb(main):077:0>+foo+bar+{+%7Carg%7C+puts+arg+}
Block+given+to+bar
Yielded+from+bar
No+block+given+to+foo
=>+"Returned+from+bar"
irb(main):078:0>+foo+bar+do+%7Carg%7C+puts+arg+end
No+block+given+to+bar
Block+given+to+foo
Returned+from+bar
=>+nil|933409|entityMap^0|E|3|I|A|1A|3|1K|3|0|0|E|3|P|3|0|0|0|0|J|3|1R|3|25|A|0|3|3|A|A|0|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|1J|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1K|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1L|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|U|3|V|5|6|7|1T|8|@$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]]|D|@]|E|$]]|$1|W|3|X|5|H|7|1Y|8|@]|D|@]|E|$I|J]]|$1|Y|3|Z|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|10|3|11|5|H|7|20|8|@]|D|@]|E|$I|J]]|$1|12|3|-4|5|6|7|21|8|@]|D|@]|E|$]]]|13|$]]

There is a subtle difference between the two syntaxes. <code>{ }</code> are higher precedence than <code>do ... end</code>. Thus, the following will pass <code>bar</code> and a block to method <code>foo</code>:

<pre><code>foo bar do ... end
</code></pre>

while the following will pass a block to <code>bar</code>, and the result of that to <code>foo</code>:

<pre><code>foo bar { ... }
</code></pre>

So your examples will act the same. However, if you left the parentheses off:

<pre><code>&gt; 3.upto 9 { 
 puts "Hi" 
}
SyntaxError: compile error
(irb):82: syntax error, unexpected '{', expecting $end
3.upto 9 { 
 ^
 from (irb):82
 from :0

&gt; 3.upto 9 do 
 puts "Hi" 
 end
Hi
Hi
Hi
Hi
Hi
Hi
Hi
=&gt; 3
</code></pre>

So, <code>{ }</code> are more likely to catch you up if you leave off parentheses in Ruby, which is fairly common; for this reason, and because Ruby conditionals and other control constructs all use <code>end</code> as a delimiter, people usually use <code>do ... end</code> for multi-line code blocks that come at the end of a statement.

However, <code>{ }</code> is frequently use in places where <code>do ... end</code> would be cumbersome, for instance, if you are chaining several methods together which take blocks. This can allow you to write short, one line little blocks which can be used as part of a method chain.

<pre><code>&gt; [1,2,3].sort{|x,y| y&lt;=&gt;x}.map{|x| x+1}
=&gt; [4, 3, 2]
</code></pre>

Here's an example to illustrate this difference:

<pre><code>def foo arg
 if block_given?
 puts "Block given to foo"
 yield arg
 else
 puts "No block given to foo"
 arg
 end
end


def bar
 if block_given?
 puts "Block given to bar"
 yield "Yielded from bar"
 else
 puts "No block given to bar"
 end
 "Returned from bar"
end

irb(main):077:0&gt; foo bar { |arg| puts arg }
Block given to bar
Yielded from bar
No block given to foo
=&gt; "Returned from bar"
irb(main):078:0&gt; foo bar do |arg| puts arg end
No block given to bar
Block given to foo
Returned from bar
=&gt; nil
</code></pre>

I’m a beginner in Ruby, so I’m sorry to ask something so simple, but is there anything wrong with this code – 

<pre><code>3.upto(9) {
 print "Hello"
 puts " World"
}
</code></pre>

or

<pre><code>3.upto(9) { |n|
 print "Hello "
 puts n
}
</code></pre>

It works well enough, but most of the code samples I see use the syntax of 

<pre><code>3.upto(9) do |n|
 print "Hello "
 puts n
end
</code></pre>

is it just the convention to only use curly braces for single statements? Coming from C/C# the first seems more natural to me, but when in Rome!

Ruby multiline block without do end

Ruby语言

我是Ruby的初学者，所以很抱歉问这么简单的问题，但是这段代码有什么问题吗？3.upto(9) {  print "Hello"  puts " World"}或3.upto(9) { |n|  print "Hello "  puts n}它工作得很好，但我看到的大多数代码示例都使用3.upto(9) do |n| ...

问不带do结尾的Ruby多行块
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