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Confusion Over Keyword Arguments

 
 
Mr. Big
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      03-01-2006
Ruby 2.0 will include new syntax for hash literals: {a:3, b:4}. However,
one can leave off the {}s to create a hash. Current software uses this
for "faked" keyword arguments.

def my_meth(options={})
end

(1) my_meth(:keyword => 3) # Ruby 1.8
(2) my_meth(keyword:3, another_option:10) # Ruby 2.0

Won't this create confusion? Why must keyword arguments use the same
syntax as new hash literals? How about "=" for keyword arguments instead
(such as in python)?

--
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Logan Capaldo
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      03-01-2006

On Mar 1, 2006, at 3:32 PM, Mr. Big wrote:

> Ruby 2.0 will include new syntax for hash literals: {a:3, b:4}.
> However,
> one can leave off the {}s to create a hash. Current software uses this
> for "faked" keyword arguments.
>
> def my_meth(options={})
> end
>
> (1) my_meth(:keyword => 3) # Ruby 1.8
> (2) my_meth(keyword:3, another_option:10) # Ruby 2.0
>
> Won't this create confusion? Why must keyword arguments use the same
> syntax as new hash literals? How about "=" for keyword arguments
> instead
> (such as in python)?
>
> --
> Posted via http://www.ruby-forum.com/.
>



Ruby doesn't have keyword arguments at all. When you call a method
with "keyword arguments" you are really just passing in a single
hash. There's no confusion because the syntaxes do the exact same thing
example_hash = { a: 1, b: 2 }
my_meth(example_hash) #pass a hash as the single argument to my_meth
my_meth(a: 1, b: 2) # pass a hash as the single argument to my_meth

Neither of these will actually set local variables, the signature for
a method like this is as follows:

def my_meth(argument_hash)
...
end

e.g.:

def my_meth(arg_hash)
arg_hash[:a] + arg_hash[:b]
end

So one would say my_meth(:a => 1, :b => 2) and get back 3
or one would say my_meth(a: 1, b: 2) and get back 3
or one would say
example_hash = { :a => 1, :b => 2 }
my_meth(example_hash) # returns 3 also



 
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Mr. Big
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      03-01-2006
> When you call a method with "keyword arguments" you are really just passing in a single hash.

Keyword arguments aren't hashes.

def my_meth(foo:, bar
foo + bar
end
my_meth(foo:3, bar:4)

# later we see this, we do not know how the method is defined.
my_meth2(arg:100, arg2:10)

There is no way to tell if my_meth2 is using a hash or keyword arguments
without looking it up. However, if keyword arguments used "=" instead,
there would be no double checking.
my_meth2(arg=100, arg2=10)

A keyword argument that takes a symbol ends up looking very ugly (I
guess "=" doesn't work well here, either):
foo(key::symbol) or
foo(key: :symbol)

--
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Jeff Cohen
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      03-01-2006
Mr. Big wrote:
> Ruby 2.0 will include new syntax for hash literals: {a:3, b:4}. However,
> one can leave off the {}s to create a hash.
>
> Won't this create confusion?


I am personally not in favor of allowing the : character instead of =>.
(The last time I checked, this new syntax was marked as highly
experimental and not a done deal yet).

With colons already in use to denote the start of a symbol name, using a
colon as a separator between a key-value pair is going to confuse many
people, especially since everyone seems to like their own whitespace
conventions.

I hope Matz reconsiders and decides that the "experiment" is not worth
it.

As an aside, I wonder why => was chosen instead of a simple = sign.
Seems like it's un-ruby-like to make us type the extra character

Jeff
www.softiesonrails.com


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dblack@wobblini.net
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      03-01-2006
Hi --

On Thu, 2 Mar 2006, Jeff Cohen wrote:

> Mr. Big wrote:
>> Ruby 2.0 will include new syntax for hash literals: {a:3, b:4}. However,
>> one can leave off the {}s to create a hash.
>>
>> Won't this create confusion?

>
> I am personally not in favor of allowing the : character instead of =>.
> (The last time I checked, this new syntax was marked as highly
> experimental and not a done deal yet).
>
> With colons already in use to denote the start of a symbol name, using a
> colon as a separator between a key-value pair is going to confuse many
> people, especially since everyone seems to like their own whitespace
> conventions.
>
> I hope Matz reconsiders and decides that the "experiment" is not worth
> it.
>
> As an aside, I wonder why => was chosen instead of a simple = sign.
> Seems like it's un-ruby-like to make us type the extra character


I don't think it's extra. I would hate to have to parse -- visually
-- things like:

hash = { a = 1, b = 2, 4 = 5 }

etc.


David

--
David A. Black ((E-Mail Removed))
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black


 
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Jeff Cohen
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      03-01-2006
David Black wrote:
> I don't think it's extra. I would hate to have to parse -- visually
> -- things like:
>
> hash = { a = 1, b = 2, 4 = 5 }


That's true. I guess I was thinking of method calls, like:

start_hockey_game(:home_team = "Chicago", :away_team = "Detroit")

In other words, in reality most of the hashes I create are implicit
hashes created when passing method arguments.

But you're right, for your canonical case, it would be bad; and that
alone probably justifies having a separate syntax for the key-value
pair.

Jeff

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Yukihiro Matsumoto
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      03-01-2006
Hi,

In message "Re: Confusion Over Keyword Arguments"
on Thu, 2 Mar 2006 05:32:50 +0900, "Mr. Big" <(E-Mail Removed)> writes:

|def my_meth(options={})
|end
|
|(1) my_meth(:keyword => 3) # Ruby 1.8
|(2) my_meth(keyword:3, another_option:10) # Ruby 2.0
|
|Won't this create confusion?

No, on the virtual implementation (only inside of my brain), they are
same things. The magic is in receiving and interpreting arguments.

|Why must keyword arguments use the same
|syntax as new hash literals?

No, we don't have to. The colon can be ugly with symbols, for
example,

db.find(order: :date)

is not good looking. Any other proposal (except for "=')?

|How about "=" for keyword arguments instead
|(such as in python)?

Unfortunately, assignments are legal in argument list in Ruby.

matz.


 
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E. Saynatkari
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      03-02-2006
Yukihiro Matsumoto wrote:
> Hi,
>
> In message "Re: Confusion Over Keyword Arguments"
> on Thu, 2 Mar 2006 05:32:50 +0900, "Mr. Big" <(E-Mail Removed)> writes:
>
> |def my_meth(options={})
> |end
> |
> |(1) my_meth(:keyword => 3) # Ruby 1.8
> |(2) my_meth(keyword:3, another_option:10) # Ruby 2.0
> |
> |Won't this create confusion?
>
> No, on the virtual implementation (only inside of my brain), they are
> same things. The magic is in receiving and interpreting arguments.
>
> |Why must keyword arguments use the same
> |syntax as new hash literals?
>
> No, we don't have to. The colon can be ugly with symbols, for
> example,
>
> db.find(order: :date)
>
> is not good looking. Any other proposal (except for "=')?


We are running out of characters, could we instead switch to
be the very first fully Unicode language? Have the actual
lambda sign for lambdas, the sigil for symbols and so on..

> |How about "=" for keyword arguments instead
> |(such as in python)?
>
> Unfortunately, assignments are legal in argument list in Ruby.
>
> matz.



E

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Yukihiro Matsumoto
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      03-02-2006
Hi,

In message "Re: Confusion Over Keyword Arguments"
on Thu, 2 Mar 2006 09:32:41 +0900, "E. Saynatkari" <(E-Mail Removed)> writes:

|We are running out of characters, could we instead switch to
|be the very first fully Unicode language? Have the actual
|lambda sign for lambdas, the sigil for symbols and so on..

Too late. Perl6 took that place.

matz.


 
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Jay Levitt
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      03-02-2006
On Thu, 2 Mar 2006 08:46:23 +0900, Yukihiro Matsumoto wrote:

> No, we don't have to. The colon can be ugly with symbols, for
> example,
>
> db.find(order: :date)
>
> is not good looking. Any other proposal (except for "=')?


If the keyword has to be unadorned, and this has to be done solely through
an infix operator, how about:

db.find (order ~> :date)
db.find (order -> :date)

If it's ok to adorn the keyword, and the parser can distinguish these, that
opens up lots of options:

db.find ([order] = :date)
db.find (|order| = :date)
db.find (-order- = :date)
db.find (/order/ = :date)
db.find (#order# = :date)
db.find (#order = :date)

I've got no clue how the parser works, so these may be non-starters for
various reasons.

Jay Levitt
 
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