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comp.lang.ruby

ternary operator confusion

Belorion

6/1/2005 4:35:00 PM

I don't know if this is "improper" use of the ternary operator, but I
am curious as to why this is happening.

Simplified example:

a = nil
true ? a = 1 : a = 2
-> a = 1

a = []
true ? a.push 1 : a.push 2 (syntax error)

Why the syntax error?

-Matt
18 Answers

Gavin Kistner

6/1/2005 4:40:00 PM

0

true ? a.push(1) : a.push(2)

Michael Campbell

6/1/2005 4:50:00 PM

0

"poetry mode" strikes again!

On 6/1/05, Phrogz <gavin@refinery.com> wrote:
> true ? a.push(1) : a.push(2)
>
>
>

Belorion

6/1/2005 5:03:00 PM

0

> "poetry mode" strikes again!
>
> On 6/1/05, Phrogz <gavin@refinery.com> wrote:
> > true ? a.push(1) : a.push(2)

ARG, now I feel dumb. Thanks for the heads up!

Marcel Molina Jr.

6/1/2005 8:50:00 PM

0

On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
> true ? a.push(1) : a.push(2)

i suspect this could have been just a contrived example but you could also
do:

a.push true ? 1 : 2

marcel
--
Marcel Molina Jr. <marcel@vernix.org>

Eric Mahurin

6/1/2005 9:21:00 PM

0

--- "Marcel Molina Jr." <marcel@vernix.org> wrote:

> On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
> > true ? a.push(1) : a.push(2)
>
> i suspect this could have been just a contrived example but
> you could also
> do:
>
> a.push true ? 1 : 2

I wish Ruby didn't make the () optional when passing args
(probably from Perl which wanted to be like shells/tcl/lisp
where command/function and arguments are space separated).

When you don't put the () in, the precendence can get confusing
and you arbitrarily prevent the first arg to start with a "("
(otherwise it will treat that "(" as what starts the argument
list).

Why do people feel the need to drop the ()? I didn't like it
in Perl and I don't like it in Ruby. Do people just want
something that is kind of like shell syntax?






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ES

6/1/2005 9:25:00 PM

0


Le 1/6/2005, "Eric Mahurin" <eric_mahurin@yahoo.com> a écrit:
>--- "Marcel Molina Jr." <marcel@vernix.org> wrote:
>
>> On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
>> > true ? a.push(1) : a.push(2)
>>
>> i suspect this could have been just a contrived example but
>> you could also
>> do:
>>
>> a.push true ? 1 : 2
>
>I wish Ruby didn't make the () optional when passing args
>(probably from Perl which wanted to be like shells/tcl/lisp
>where command/function and arguments are space separated).
>
>When you don't put the () in, the precendence can get confusing
>and you arbitrarily prevent the first arg to start with a "("
>(otherwise it will treat that "(" as what starts the argument
>list).
>
>Why do people feel the need to drop the ()? I didn't like it
>in Perl and I don't like it in Ruby. Do people just want
>something that is kind of like shell syntax?

Less typing, uniform access, etc. Good news is that if one does
want to use parens, one is welcome to not do so.

E

--
template<typename duck>
void quack(duck& d) { d.quack(); }

Austin Ziegler

6/1/2005 9:48:00 PM

0

On 6/1/05, Eric Mahurin <eric_mahurin@yahoo.com> wrote:
> --- "Marcel Molina Jr." <marcel@vernix.org> wrote:
>> On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
>>> true ? a.push(1) : a.push(2)
>> i suspect this could have been just a contrived example but you
>> could also do:
>>
>> a.push true ? 1 : 2
> I wish Ruby didn't make the () optional when passing args
> (probably from Perl which wanted to be like shells/tcl/lisp where
> command/function and arguments are space separated).
>
> When you don't put the () in, the precendence can get confusing
> and you arbitrarily prevent the first arg to start with a "("
> (otherwise it will treat that "(" as what starts the argument
> list).
>
> Why do people feel the need to drop the ()? I didn't like it in
> Perl and I don't like it in Ruby. Do people just want something
> that is kind of like shell syntax?

I use it in PDF::Writer because it makes certain parts feel more
like a DSL (domain specific language) than a program.

When I release this (later this week, I *hope*), it'll be visible in
the quickref code.

-austin
--
Austin Ziegler * halostatue@gmail.com
* Alternate: austin@halostatue.ca

Jamis Buck

6/1/2005 9:52:00 PM

0

On Jun 1, 2005, at 3:47 PM, Austin Ziegler wrote:

> On 6/1/05, Eric Mahurin <eric_mahurin@yahoo.com> wrote:
>
>> --- "Marcel Molina Jr." <marcel@vernix.org> wrote:
>>
>>> On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
>>>
>>>> true ? a.push(1) : a.push(2)
>>>>
>>> i suspect this could have been just a contrived example but you
>>> could also do:
>>>
>>> a.push true ? 1 : 2
>>>
>> I wish Ruby didn't make the () optional when passing args
>> (probably from Perl which wanted to be like shells/tcl/lisp where
>> command/function and arguments are space separated).
>>
>> When you don't put the () in, the precendence can get confusing
>> and you arbitrarily prevent the first arg to start with a "("
>> (otherwise it will treat that "(" as what starts the argument
>> list).
>>
>> Why do people feel the need to drop the ()? I didn't like it in
>> Perl and I don't like it in Ruby. Do people just want something
>> that is kind of like shell syntax?
>>
>
> I use it in PDF::Writer because it makes certain parts feel more
> like a DSL (domain specific language) than a program.

And that is _precisely_ why I like the technique as well. It is
wonderful for making a Ruby program read (more or less) like a domain
document. And when ambiguity raises its ugly head, I can always throw
in the parens to disambiguate.

But as someone else pointed out, if you don't like it, no one is
forcing you to drop the parens in your own programs. Choose the
technique that works best for you.

- Jamis

Charles Hixson

6/1/2005 10:43:00 PM

0

ES wrote:

>Le 1/6/2005, "Eric Mahurin" <eric_mahurin@yahoo.com> a écrit:
>
>
>>--- "Marcel Molina Jr." <marcel@vernix.org> wrote:
>>
>>
>>
>>>On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
>>>
>>>
>>>>true ? a.push(1) : a.push(2)
>>>>
>>>>
>>>i suspect this could have been just a contrived example but
>>>you could also
>>>do:
>>>
>>>a.push true ? 1 : 2
>>>
>>>
>>I wish Ruby didn't make the () optional when passing args
>>(probably from Perl which wanted to be like shells/tcl/lisp
>>where command/function and arguments are space separated).
>>
>>When you don't put the () in, the precendence can get confusing
>>and you arbitrarily prevent the first arg to start with a "("
>>(otherwise it will treat that "(" as what starts the argument
>>list).
>>
>>Why do people feel the need to drop the ()? I didn't like it
>>in Perl and I don't like it in Ruby. Do people just want
>>something that is kind of like shell syntax?
>>
>>
>
>Less typing, uniform access, etc. Good news is that if one does
>want to use parens, one is welcome to not do so.
>
>E
>
>--
>template<typename duck>
>void quack(duck& d) { d.quack(); }
>
>
>
>
Uniform access could have been achieved if only () was made optional.
(A good choice in my mind.) OTOH, I'm not that happy with optional
parenthesis where the parameters are required. To me that feels like a
bad design choice. (And with some type faces the difference between
(stuff) and {stuff} isn't all that obvious. But that's a font
problem...mainly.)

Eric Mahurin

6/1/2005 10:51:00 PM

0

--- Jamis Buck <jamis@37signals.com> wrote:

> On Jun 1, 2005, at 3:47 PM, Austin Ziegler wrote:
>
> > On 6/1/05, Eric Mahurin <eric_mahurin@yahoo.com> wrote:
> >
> >> --- "Marcel Molina Jr." <marcel@vernix.org> wrote:
> >>
> >>> On Thu, Jun 02, 2005 at 01:40:23AM +0900, Phrogz wrote:
> >>>
> >>>> true ? a.push(1) : a.push(2)
> >>>>
> >>> i suspect this could have been just a contrived example
> but you
> >>> could also do:
> >>>
> >>> a.push true ? 1 : 2
> >>>
> >> I wish Ruby didn't make the () optional when passing args
> >> (probably from Perl which wanted to be like
> shells/tcl/lisp where
> >> command/function and arguments are space separated).
> >>
> >> When you don't put the () in, the precendence can get
> confusing
> >> and you arbitrarily prevent the first arg to start with a
> "("
> >> (otherwise it will treat that "(" as what starts the
> argument
> >> list).
> >>
> >> Why do people feel the need to drop the ()? I didn't like
> it in
> >> Perl and I don't like it in Ruby. Do people just want
> something
> >> that is kind of like shell syntax?
> >>
> >
> > I use it in PDF::Writer because it makes certain parts feel
> more
> > like a DSL (domain specific language) than a program.
>
> And that is _precisely_ why I like the technique as well. It
> is
> wonderful for making a Ruby program read (more or less) like
> a domain
> document. And when ambiguity raises its ugly head, I can
> always throw
> in the parens to disambiguate.
>
> But as someone else pointed out, if you don't like it, no one
> is
> forcing you to drop the parens in your own programs. Choose
> the
> technique that works best for you.

When I first starting using Perl (v4) I thought it was neat
that I didn't need the parens, but then I got burned a few
times when I needed parens in the first arg. Then I realized
what an ugly hack at in the syntax this was. This was a bad
thing that was brought over from perl. Consider the following
method calls:

1. f a , b # OK
2. f a , (b) # OK
3. f (a)+0, b # *** now (a) looks like the args to f***
4. f 0+(a), b # putting in the 0+ prevented the problem above

The problem is if you start with #1, you may eventually need
for the the first arg to be some expression and you run into
#3.

For comparision here ways that some languages make
function/method/procedure/command calls:

function/method/procedure/command: f
arguments: a, b

`f a b` shells (bash also supports "$(f a b)")
[f a b] tcl
(f a b) lisp
f(a,b) most other languages including perl and ruby
f a,b alternate for perl and ruby

The problem is that perl/ruby support both of the last 2 forms.
This results in ambiguity if you are trying to use the last
form, but need argument "a" to start with a "(". The () form
wins the ambiguity in this case. The "f a,b" form could have
worked more cleanly if the "f(a,b)" form wasn't supported
(you'd have to group with "(f a,b)"). But since perl/ruby
supports both and the f(a,b) form wins ambiguities, the f a,b
form looks to work inconsistently. On top of that you have to
think about precedence more closely (what started this thread).

just my 2 cents.




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