Hi sir Gavin Sinclair [mailto:gsinclair@soyabean.com.au]
You wrote:
[On ‘and’ and ‘&&’]
I am surprise and I’m new to Ruby 
I do find both structurally same, but why the difference in
precedence?
Pls enlighten…
Not so long ago, Matz stated that the difference in
precedence was because natural language doesn’t observe a
high precedence for ‘and’. I thought that was a very nice
observation from a computer geek.
but the precedence of the assignment operator has always been low (my
experience only) in other languages.
Eg, x = a and (b or c) and not c
would mean putting/assigning all results (ultimately) to x…
Am I confusing “=” assignment with “=” comparison then??
Anyway, if you get any more authoriatitive answers (I may be
confusing the issue with something else :), this one should be a FAQ.
Many thanks.
Cheers,
Gavin
Kind regards,
-botp
Hi sir Gavin Sinclair [mailto:gsinclair@soyabean.com.au]
You wrote:
[On ‘and’ and ‘&&’]
I am surprise and I’m new to Ruby
I do find both structurally same, but why the difference in
precedence?
Pls enlighten…
Not so long ago, Matz stated that the difference in
precedence was because natural language doesn’t observe a
high precedence for ‘and’. I thought that was a very nice
observation from a computer geek.
but the precedence of the assignment operator has always been low (my
experience only) in other languages.
Eg, x = a and (b or c) and not c
would mean putting/assigning all results (ultimately) to x…
Am I confusing “=” assignment with “=” comparison then??
No, but other languages don’t typically have ‘and’ and ‘&&’. So yes, ‘=’ has a
low precedence, but ‘and’ is lower. To achieve your example you use ‘&&’. If
Ruby had no ‘and’ it wouldn’t be confusing. Likewise if ‘and’ was just sugar
for ‘&&’. AFAIK, no other langugage is like Ruby in this regard, so it’s bound
to be confusing at least once. I believe Matz has designed it correctly,
though. ‘and’ and ‘&&’ are subtly different and can be used to communicate
different programmer intent:
result = value && value.size
param = param || default_value
action() and consequent_action()
action() or alternative_action()
Without thinking about precedence, the code above just reads nicely: the
subtleties of the intended high-level intention are communicated very well
through the symbols used.
Gavin
···
From: “Peña, Botp” <botp@delmonte-phil.com
It also works very well if you do:
param = param || default_value and handle(param)
This way, handle(param) is only called if the result of param ||
default_value is true.
-austin
– Austin Ziegler, austin@halostatue.ca on 2002.11.21 at 09.51.47
···
On Thu, 21 Nov 2002 20:45:30 +0900, Gavin Sinclair wrote:
result = value && value.size
param = param || default_value
action() and consequent_action()
action() or alternative_action()
Without thinking about precedence, the code above just reads
nicely: the subtleties of the intended high-level intention are
communicated very well through the symbols used.