From: Logan Capaldo <logancapaldo@...>
Date: 2006-03-27T08:04:30+09:00
Subject: Re: deciphering poignant guide chapter 4 example

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On Mar 26, 2006, at 5:43 PM, john_sips_tea@yahoo.com wrote:

> I'll have to think about that. I don't see the connection between
> strings and method lookup. In Python code, you write a name(),
> and python works its way up the inheritance tree looking for
> the function definition. You can't call a method like:
>
> def my_func():
>     print "hi"
> foo = "my_func"
> foo()  # Trying to call my_func, but it fails.
>
> so I don't see the string/method-call connection you're
> referring to...

As a little aside, python lets you do:

def z(x):
	print x

a = z

a("Hello")
Hello

yes?

well ruby as you know, makes parens optional in method calls, what  
this means is you can't directly assign methods around. So in ruby  
you can do this:
send("z", "Hello")

or this
send(:z, "Hello")

In the first case, z has to be hashed to its numeric symbol code at  
run time. This means somewhere inside the send method, its doing  
"z".to_sym. When you use :z, the hash is computed at compile time,  
and you're basically passing send a number, let's say 9.

send(9, "Hello")

In ruby Symbols don't have the extra level of indirection that  
strings do. "z" is a pointer to the string object that contains the  
character 'z'. :z is the number 9. (well not really, but it is *a*  
number).

This is a reason for using symbols as hash keys, if you never display  
the keys for instance. Its a number so equality comparsions become  
trivial and hashing operations also become cheaper (I imagine so  
anyway).
  Using symbols basically saves you one level of runtime lookup.



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