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<title>Ruby FAQ:
Syntax
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<h2><a name="s4">4.
Syntax
</a></h2>
<h2><a name="ss4.1">4.1
What does <code>:exit</code> mean?
</a></h2>
It is an integer(Fixnum) called a symbol which corresponds one to one
with the identifier. "exit".intern gives the same integer.
"catch", "throw", "autoload", etc, require a string or a symbol as
an argument.
<br><br>
"method_missing", "method_added" and "singleton_method_added"
requires a symbol.
<h2><a name="ss4.2">4.2
How can I access the value of a symbol?
</a></h2>
In the scope of "symbol", do "eval((:symbol).id2name)".
<blockquote><code><pre>
a = 'This is the content of "a"'
b = eval(:a.id2name)
a.id == b.id
</pre></code></blockquote>
<h2><a name="ss4.3">4.3
Is <code>loop</code> a control structure?
</a></h2>
It is a method defined in <code>Kernel</code>. The block which follows introduces
a new scope for local variables.
<h2><a name="ss4.4">4.4
<code>a +b</code> gives an error.
</a></h2>
It is parsed as <code>a(+b)</code>. Remove the space to the left of <code>+</code>
or add a space to the right of <code>+</code>.
<h2><a name="ss4.5">4.5
<code>s = "x"; puts s *10</code> gives an error.
</a></h2>
It is parsed as puts(s(*10)). Let the expression s*10 or s * 10.
<h2><a name="ss4.6">4.6
Nothing appears with <code>p {}</code>.
</a></h2>
{} is parsed as a block, not a constructor of Hash. Let it <code>p({})</code>.
<h2><a name="ss4.7">4.7
After <code>def pos= (val) print @pos,"\n"; @pos = val end</code>,
I cannot use the method <code>pos = 1</code>.
</a></h2>
Methods with <code>=</code> appended are called in a receiver form. Invoke it as
<code>self.pos = 1</code>.
<h2><a name="ss4.8">4.8
What is the difference between <code>'\1'</code> and <code>'\\1'</code>?
</a></h2>
They are the same meaning. In a singlequote string, Only <code>\'</code> and
<code>\\</code> are transformed and other combinations remain unchanged.
<h2><a name="ss4.9">4.9
<code>p true or true and false</code> prints <code>true</code>, while
<code>a=true if true or true and false</code> does not assign <code>true</code>
to <code>a</code>.
</a></h2>
The first expression is parsed as <code>(p true) or true and false</code>.
<code>and/or</code> is not parsed as an element of the argument of <code>p</code>
but an element of an expression.
<br><br>
The second is parsed as a=true if (true or true and false).
"if" has a lower priority than "and/or". "and" and "or" has the
same priority and parsed from left to right.
<h2><a name="ss4.10">4.10
<code>p(nil || "")</code> returns "", while <code>p(nil or "")</code>
gives parse error.
</a></h2>
|| can conbine arguments. <code>or</code> combines only expressions,
not arguments.
Try <code>p nil or ""</code> and <code>p((nil or ""))</code>.
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