Asp Forum - Re: is it behaving strange ?

hemant

2/15/2007 3:11:00 PM

On 2/15/07, sur max <sur.max@gmail.com> wrote:
> *a = 9 # => [9]
> a # => [9]
> *a # => compile error
> *b=*a # => [9]
> *b = a # => [[9]]
> b = a # => [9]
> b = *a # => 9 ----- this is amazing ?

Splat operator is amazing, but above behaviour can be explained using this:

"If the last lvalue is preceded by an asterisk, all the remaining
rvalues will be collected and
assigned to that lvalue as an array. Similarly, if the last rvalue is
an array, you can
prefix it with an asterisk, which effectively expands it into its
constituent values in
place. (This is not necessary if the rvalue is the only thing on the
right side—the array
will be expanded automatically.)
"
See, nothing wierd out there. ;)

PS: Taken from PickAxe Verbatim.

--
gnufied
-----------
There was only one Road; that it was like a great river: its springs
were at every doorstep, and every path was its tributary.
http://people.inxsasia.c...

16 Answers

dblack

2/15/2007 3:30:00 PM

hemant

2/15/2007 4:23:00 PM

On 2/15/07, sur max <sur.max@gmail.com> wrote:
> ok and its like ....
>
> *a = 9

remember a would become an array here.because as explained above,if
lvalue is prefixed with asterisk, then rvalue is collected and
assigned to lvalue as an array.

> a << 5

append 5 to a (which is an array)

> b = *a # => [9,5]
> is there any relation in this n above ?

Now, above is pretty standard ruby behaviour, it has nothing to do
with * operator, as usual * extracts the values from a(which was an
array).

For example:

irb(main):062:0> b = 9,5
[9, 5]
irb(main):063:0> b
[9, 5]
irb(main):064:0> b,c = 9,5
[9, 5]
irb(main):065:0> b
9
irb(main):066:0> c
5

>
> On 2/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
> >
> > Hi --
> >
> > On Fri, 16 Feb 2007, hemant wrote:
> >
> > > On 2/15/07, sur max <sur.max@gmail.com> wrote:
> > >> *a = 9 # => [9]
> > >> a # => [9]
> > >> *a # => compile error
> > >> *b=*a # => [9]
> > >> *b = a # => [[9]]
> > >> b = a # => [9]
> > >> b = *a # => 9 ----- this is amazing ?
> > >
> > > Splat operator is amazing, but above behaviour can be explained using
> > this:
> > >
> > > "If the last lvalue is preceded by an asterisk, all the remaining
> > > rvalues will be collected and
> > > assigned to that lvalue as an array. Similarly, if the last rvalue is
> > > an array, you can
> > > prefix it with an asterisk, which effectively expands it into its
> > > constituent values in
> > > place. (This is not necessary if the rvalue is the only thing on the
> > > right side—the array
> > > will be expanded automatically.)
> > > "
> > > See, nothing wierd out there. ;)
> >
> > Another way to look at it, which I think covers all of the above
> > cases, is:
> >
> > *x equals [x] without the []
> >
> > So:
> >
> > *a = 9 # a without the [] is 9, so a == [9]
> > *b = a # b without the [] is [9], so b == [[9]]
> > b = *a # b == [9] without the [], so b == 9
> >
> >
> > That's why I call it the "unary unarray" operator.
> >
> >
> > David
> >
> > --
> > Q. What is THE Ruby book for Rails developers?
> > A. RUBY FOR RAILS by David A. Black (http://www.manning...)
> > (See what readers are saying! http://www.r.../r...)
> > Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> > A. Ruby Power and Light, LLC (http://www.r...)
> >
>
>
>
> --
> sur
> http://expr...
>

--
gnufied
-----------
There was only one Road; that it was like a great river: its springs
were at every doorstep, and every path was its tributary.
http://people.inxsasia.c...

hemant

2/15/2007 5:25:00 PM

On 2/15/07, sur max <sur.max@gmail.com> wrote:
> Thats pretty known.
> And even this too...

Again, I am sorry to bore you with little known things. ;)

> a = 2,3,4,5,6 # => [2,3,4,5,6]
>
> b, = a --- now this is beauty
> b # => 2
> b,c = a
> b # => 2
> c # => 3
> and so...
> b,c,d = a
>
> but still didnt get clear .... is it like we can use *a for assigning to
> some other var ONLY ?

I would like to think so, thats why we got syntax error exception
tossed at our face when we do:

*a = 9
*a

I guess ruby interpretor is doing tough job of differentiating splat
from multiplication operator and it decided to not allow you to do
that.

However, you can very well do

a = 9
+a
++a
-a

Again, I might be stating the obvious. ;)

> On 2/15/07, hemant <gethemant@gmail.com> wrote:
> >
> > On 2/15/07, sur max <sur.max@gmail.com> wrote:
> > > ok and its like ....
> > >
> > > *a = 9
> >
> > remember a would become an array here.because as explained above,if
> > lvalue is prefixed with asterisk, then rvalue is collected and
> > assigned to lvalue as an array.
> >
> > > a << 5
> >
> > append 5 to a (which is an array)
> >
> > > b = *a # => [9,5]
> > > is there any relation in this n above ?
> >
> > Now, above is pretty standard ruby behaviour, it has nothing to do
> > with * operator, as usual * extracts the values from a(which was an
> > array).
> >
> > For example:
> >
> > irb(main):062:0> b = 9,5
> > [9, 5]
> > irb(main):063:0> b
> > [9, 5]
> > irb(main):064:0> b,c = 9,5
> > [9, 5]
> > irb(main):065:0> b
> > 9
> > irb(main):066:0> c
> > 5
> >
> >
> >
> >
> > >
> > > On 2/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
> > > >
> > > > Hi --
> > > >
> > > > On Fri, 16 Feb 2007, hemant wrote:
> > > >
> > > > > On 2/15/07, sur max <sur.max@gmail.com> wrote:
> > > > >> *a = 9 # => [9]
> > > > >> a # => [9]
> > > > >> *a # => compile error
> > > > >> *b=*a # => [9]
> > > > >> *b = a # => [[9]]
> > > > >> b = a # => [9]
> > > > >> b = *a # => 9 ----- this is amazing ?
> > > > >
> > > > > Splat operator is amazing, but above behaviour can be explained
> > using
> > > > this:
> > > > >
> > > > > "If the last lvalue is preceded by an asterisk, all the remaining
> > > > > rvalues will be collected and
> > > > > assigned to that lvalue as an array. Similarly, if the last rvalue
> > is
> > > > > an array, you can
> > > > > prefix it with an asterisk, which effectively expands it into its
> > > > > constituent values in
> > > > > place. (This is not necessary if the rvalue is the only thing on the
> > > > > right side—the array
> > > > > will be expanded automatically.)
> > > > > "
> > > > > See, nothing wierd out there. ;)
> > > >
> > > > Another way to look at it, which I think covers all of the above
> > > > cases, is:
> > > >
> > > > *x equals [x] without the []
> > > >
> > > > So:
> > > >
> > > > *a = 9 # a without the [] is 9, so a == [9]
> > > > *b = a # b without the [] is [9], so b == [[9]]
> > > > b = *a # b == [9] without the [], so b == 9
> > > >
> > > >
> > > > That's why I call it the "unary unarray" operator.
> > > >
> > > >
> > > > David
> > > >
> > > > --
> > > > Q. What is THE Ruby book for Rails developers?
> > > > A. RUBY FOR RAILS by David A. Black (http://www.manning...)
> > > > (See what readers are saying! http://www.r.../r...)
> > > > Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> > > > A. Ruby Power and Light, LLC (http://www.r...)
> > > >
> > >
> > >
> > >
> > > --
> > > sur
> > > http://expr...
> > >
> >
> >
> > --
> > gnufied
> > -----------
> > There was only one Road; that it was like a great river: its springs
> > were at every doorstep, and every path was its tributary.
> > http://people.inxsasia.c...
> >
> >
>
>
> --
> sur
> http://expr...
>

--
gnufied
-----------
There was only one Road; that it was like a great river: its springs
were at every doorstep, and every path was its tributary.
http://people.inxsasia.c...

dblack

2/15/2007 6:40:00 PM

Jacob Fugal

2/15/2007 6:41:00 PM

On 2/15/07, sur max <sur.max@gmail.com> wrote:
> *a = 9 # i like this number :)
...
> a << 5
> b = *a # => [9,5] ------- an Array
> here it seems false "*x equals [x] without the []"

Actually, the "rule" still applies, in that:

b = *a # where a = [9, 5]

and

b = 9, 5

Have the same effect. You were just forgetting to consider that b
would just slurp them back into an array.

> *a # => compile error

This seems to be the only remaining "anomaly".

Jacob Fugal

dblack

2/15/2007 6:44:00 PM

dblack

2/15/2007 6:44:00 PM

dblack

2/15/2007 7:46:00 PM

Robert Dober

2/15/2007 9:44:00 PM

On 2/15/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
> Hi --
>
> On Fri, 16 Feb 2007, Robert Dober wrote:
>
> > Well I cannot speak for OP but what puzzles me is
> >
> > a=[42] # sorry 9 is not the number ;)
> > *a ==> error # gotta check with 1.9 an 2.0 at home
> >
> > I would think that this expression can/could/should/might perfectly
> > evaluate to 42 look at this other oddity the following code is
> > completely legal and POLS(1)
> > def x *args
> > return *args
> > end
> > (1) in the sense that a,b,c = x 1,2,3 sets a to 1, b to 2 and c to 3
> > and x is a NOP
> >
> > but return in the last statement is optional, or is it not ;) I know
> > you are not falling into my trap !
> >
> > I see no reason however why
> > def x *args
> > *args
> > end
> > should not be legal
>
> I can't think of a case where you'd need it, since the arguments would
> just get wrapped up in an array anyway.
Agreed, but that was *not* my point
> Also, *args is basically
> equivalent to a bare list, and you can't do:
>
> def x
> 1,2,3
> end
>
def x
return 1,2,3
end
is legal it all is about consistency

1,2,3 vs. return 1,2,3
*rhs vs. lhs = *rhs

I have no idea if one could make it work without breaking a parsable
syntax, I just thought that OP was doing a good job at pointing to
this inconsistency.

We could forbid return *a but can we forbid lhs = *rhs?

I realize I am not smart enough to complain, - and too tired too :( -.
But I also feel that I did not really underline the inconsistency in
the syntax so far.
An inconsistency that is not really troubling me but which is here nevertheless.

Well that is pretty much what I wanted to say.

Cheers
Robert
>
> David
>
> --
> Q. What is THE Ruby book for Rails developers?
> A. RUBY FOR RAILS by David A. Black (http://www.manning...)
> (See what readers are saying! http://www.r.../r...)
> Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> A. Ruby Power and Light, LLC (http://www.r...)
>
>

--
We have not succeeded in answering all of our questions.
In fact, in some ways, we are more confused than ever.
But we feel we are confused on a higher level and about more important things.
-Anonymous

Peña, Botp

2/16/2007 5:19:00 AM

fr: sur max [mailto:sur.max@gmail.com] :
# b = [*a,6] # => [9,5,6] ----- false, compile error
# b = *a,6 # => [9,5,6] ----- false, compile error

pls be careful. "*" op will splat. so here ruby is just telling/policing you not too.

I always treat splat op as a black hole. this way i make less mistakes.

eg

so this is allowed,

irb(main):050:0> b,*a=1,2,3,4
=> [1, 2, 3, 4]
irb(main):052:0> a
=> [2, 3, 4]

this one is not,

irb(main):053:0> b,*a,c=1,2,3,4
SyntaxError: compile error
(irb):53: syntax error, unexpected ',', expecting '=' b,*a,c=1,2,3,4
irb(main):054:0>

ruby, is telling me that "*a" is a blackhole. The c does "not matter".

so is this one,

irb(main):056:0> *a
SyntaxError: compile error
(irb):56: syntax error, unexpected '\n', expecting '='

that's a blackhole without a hole or opening. feed it :)
again, another stupid blackhole reasoning.

nonetheless, splat is a very sweet yet too powerful operator. I feel that splat op digress oo-ness. But i believe it's not oo for oo's sake. It's solving problems and discovering brilliant solutions. Ruby does it w ease and fun. Sometimes, i feel ruby will trend toward object and method unification, wherein objects can be methods and vice versa. arggh, like matter <==> energy. maybe, a superproc or superlamdba in the future... i'll stop now :)

drive w caution, (black)holes ahead.

sorry for the long post fr a nuby.
kind regards -botp

comp.lang.ruby

Re: is it behaving strange ?

hemant

dblack

hemant

hemant

dblack

Jacob Fugal

dblack

dblack

dblack

Robert Dober

Peña, Botp

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