From: Lionel Thiry <lthiryidontwantspams@...>
Date: 2005-12-01T20:27:32+09:00
Subject: Re: If like smalltalk

Jules Jacobs a 辿crit :
> Hi, I have a question about Ruby if constructs. Why aren't they like 
> smalltalk if's, where you have a boolean class and two subclasses: true 
> and false. They both have these methods: ifTrue and ifFalse. If you use 
> a block with a ifTrue on a True object, it will be yielded. If you use 
> it on a false object, nothing will happen.
> 
> So in ruby code:
> 
> true.if_true do
> #code will be executed
> end
> 
> and:
> false.if_true do
> #code will NOT be executed
> end
> 
> and if_false is available too.
> 
> so you can do this too:
> 
> (var == 'a').if_true do
> puts 'var = "a"'
> end
> 
> I know it would be difficult to do an if-else thing with this because 
> the return value from the block would be the receiver:
> 
> (var == 'a').if_true do
>    puts 'var = "a"'
> end.if_false do
>    #code
> end
> 
> So is this the reason for if(var == 'a') not being syntactic sugar for 
> (var == 'a').if_true?
> 
> Thanks for answering!
> 
> Jules
> 

(var == 'a').if_true?
is parsed as a method call and then needs a method dispatch

if var =='a'
is an unambigous imperative instruction and then already understood at
parse time


SmallTalk is intellectually pure OO, while Ruby is purely practical OO
hence the difference. :)

-- 
Lionel Thiry

Personal web site: http://users.skynet.be/lthiry/