From: Brian Candler <b.candler@...>
Date: 2010-04-15T05:33:25+09:00
Subject: Re: I thought spaces didn't matter around operators

Sarah Allen wrote:
>>> 1 + 1
> is the same as
>>> 1.send(:+, 1)

Yes.

>>> 1 +1
> is the same as...?

Same again, as you have shown.

> So, in what way is 1 +2 not like 1 +t (where t is a Time object).

Well, it must be either
  (1) + (t)
or
  (1) (+t)

The Ruby parser is picking the second, even though it doesn't make sense 
at a higher level (you can't have two adjacent expressions without an 
intervening operator)

That doesn't explain why 1 +2 is treated differently though.

Actually, there is an optimisation that numeric literals have any unary 
prefix interpreted by the parser. That is, +1 is the value +1, not 1 
with a unary plus applied.

You can demonstrate it thus:

>> class Integer
>> def +@
>> puts "Whee!"
>> self
>> end
>> end
=> nil
>> +1
=> 1
>> +(1)
Whee!
=> 1
>> 

(BTW, I don't recommend redefining core class operators like this. If 
you redefine Fixnum#+, and don't preserve its existing semantics, nasty 
things will happen)

The first case doesn't invoke the unary plus method, it's just absorbed 
into the literal number.

So you'd think even more that 1 +1 would be taken as two adjacent 
integers, like 1 1 or 1 +t. Clearly, it isn't.

Welcome to Ruby. It's like your granny - it might have some warts, but 
it's an old friend.
-- 
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