make (a < b < c) illegal?

[Derek Parnell]

On Wed, 07 Feb 2007 16:55:15 -0800, Walter Bright wrote:

> Right now, in D (as well as C and C++), when you see the expression:
> 
> 	if (a < b < c)
> 
> what is your first thought? Mine is that it was written by a newbie who 
> didn't realize that (a < b) returns true or false, and that it does NOT 
> mean ((a < b) && (b < c)). The odds approach certainty that this is a 
> logic error in the code, and even if it was intentional, it raises such 
> a red flag that it shouldn't be used anyway.
> 
> Andrei has proposed (and I agreed) that this should be done away with in 
> the language, i.e. comparison operators should no longer be associative. 
>   It's a simple change to the grammar. If one really did want to write 
> such code, it could be done with parentheses:
> 
> 	if ((a < b) < c)
> 
> to get the original behavior. At least, that looks intentional.
> 
> I don't think this will break existing code that isn't already broken.

First thought: Yes, your proposed change makes sense.

Second thought: Why not make it do what the coder is wanting it to do?
   Namely, make the idiom:

     expression1 relopA expression2 relopB expression3

   translate as

     ( auto temp = expression2,
      (expression1 relopA temp) && (temp relopB expression3) )


-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Justice for David Hicks!"
8/02/2007 12:01:13 PM