List assignment syntax

[Zsban Ambrus]

I'm a little dissatisfied with the list assignment syntax of ruby.
On an example:

irb(main):001:0> a = [2, [3, 5], 8]
=> [2, [3, 5], 8]

This works:

irb(main):002:0> x, (y, ), z = a
=> [2, [3, 5], 8]

But this doesn't, although I'd like to use it instead of the above.

irb(main):003:0> x, (y), z = a
SyntaxError: compile error
(irb):3: syntax error
x, (y), z = a
^
from (irb):3

None of these work, so I know of no simple way to ignore an array element:

irb(main):004:0> x, (), z = a
SyntaxError: compile error
(irb):4: syntax error
x, (), z = a
^
from (irb):4
irb(main):005:0> x, (, ), z = a
SyntaxError: compile error
(irb):5: syntax error
x, (, ), z = a
^
(irb):5: syntax error
from (irb):5
irb(main):006:0>

These flexible list forms could imo be very useful. If ruby had the
array slicing idioms found in other languages (eg perl, mathematica),
for example if `a[[0, 2]]' returned `[a[0], a[2]]', there wouldn't
be so much need to this, as one would just say `x, z = a[[0, 2]]'.
(Does ruby have such a slicing method built in that I'm unaware of?)

I'd like to see your opinion about whether you think this kind of lhs syntax
are worth to be added to ruby, and especially whether it can cause any kind of
syntax ambugnuity or confusion.


And at last, two quick random thoughts:

1. Why does parse.y have the declaration `%token tRPAREN' if that token
type is apparently never used? (Even bison shows unused tokens in the
output file if called with -d.)

2. It would be nice if irb printed a linefeed if you quit the readline
prompt by pressing control-d. This way it causes the shell prompt to be
printed in the same line as the ruby prompt. This, of course, causes
problem only to non-windows users that quit with control-d instead of
exit, and have readline in irb, which is a minority, but still...


Thanks in advance,

ambrus

 

[Zsban Ambrus]

None of these work, so I know of no simple way to ignore an array element:
irb(main):004:0> x, (), z = a
irb(main):005:0> x, (, ), z = a

Sorry, I've just found that this works instead: x, (*), z = a

ambrus

 

[Andrew Johnson]

These flexible list forms could imo be very useful. If ruby had the
array slicing idioms found in other languages (eg perl, mathematica),
for example if `a[[0, 2]]' returned `[a[0], a[2]]', there wouldn't
be so much need to this, as one would just say `x, z = a[[0, 2]]'.
(Does ruby have such a slicing method built in that I'm unaware of?)

a = %w|help this foo perhaps bar does|
puts a.values_at(-1,1,3,0)

regards,
andrew

 

[Florian Gross]

I'm a little dissatisfied with the list assignment syntax of ruby.
On an example:

irb(main):001:0> a = [2, [3, 5], 8]
=> [2, [3, 5], 8]

This works:

irb(main):002:0> x, (y, ), z = a
=> [2, [3, 5], 8]

Personally, I would like being able to assign to nil in that case. I've
seen "_" been used as a throw away assignment target, but that's just
not as expressive as "nil", IMHO.

 

[Martin DeMello]

a = %w|help this foo perhaps bar does|
puts a.values_at(-1,1,3,0)

Is there any reason this can't be changed to a.at(1,2,3,4)? It'd make
for a more consistent feel than specialcasing the one-argument case.

martin

 

[trans. (T. Onoma)]

On Saturday 08 January 2005 11:46 am, Martin DeMello wrote:
| > a = %w|help this foo perhaps bar does|
| > puts a.values_at(-1,1,3,0)
|
| Is there any reason this can't be changed to a.at(1,2,3,4)? It'd make
| for a more consistent feel than specialcasing the one-argument case.
|
| martin

Problem is with what gets returned.

a=[1,2,5,7]
a.at(1) => 2
a.values_at(1) => [2]

T.

 

[trans. (T. Onoma)]

| > I'm a little dissatisfied with the list assignment syntax of ruby.
| > On an example:
| >
| > irb(main):001:0> a = [2, [3, 5], 8]
| > => [2, [3, 5], 8]
| >
| > This works:
| >
| > irb(main):002:0> x, (y, ), z = a
| > => [2, [3, 5], 8]
|
| Personally, I would like being able to assign to nil in that case. I've
| seen "_" been used as a throw away assignment target, but that's just
| not as expressive as "nil", IMHO.

That seems like a good idea.
T.