[ruby-talk:444061] A simple question about arguments

ruby-talk
1

Sorry for this newbie question.
For arguments to ruby methods, what's difference between these two?

method(x:y)
method(x=>y)

Thanks

···

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2

Quoting Henry R via ruby-talk (ruby-talk@ml.ruby-lang.org):

Sorry for this newbie question.
For arguments to ruby methods, what's difference between these two?

method(x:y)
method(x=>y)

x:y is a shorthand for :x=>y. That is: a hash with one element, that
has as key *symbol* :x, and as value whatever is in variable y. In the
second case, the key of the hash is whatever you have currently in
variable x.

If you have this short script:

--8<----8<----8<----8<--
def m(h)
  pp h
  pp h.class
  pp h.keys[0]
  pp h.keys[0].class
end

x=1
y=2

m(x=>y)
print("\n")
m(x:y)
--8<----8<----8<----8<--

and run it, you obtain

{1=>2}
Hash
1
Integer

{:x=>2}
Hash
:x
Symbol

HTH

Carlo

···

Subject: [ruby-talk:444061] A simple question about arguments
  Date: Sat 17 Dec 22 06:34:17AM +0000

--
  * Se la Strada e la sua Virtu' non fossero state messe da parte,
* K * Carlo E. Prelz - fluido@fluido.as che bisogno ci sarebbe
  * di parlare tanto di amore e di rettitudine? (Chuang-Tzu)
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3

that's right. Thanks.

···

Subject: [ruby-talk:444061] A simple question about arguments
Date: Sat 17 Dec 22 06:34:17AM +0000

Quoting Henry R via ruby-talk (ruby-talk@ml.ruby-lang.org):

>
> Sorry for this newbie question.
> For arguments to ruby methods, what's difference between these two?
>
> method(x:y)
> method(x=>y)
>

x:y is a shorthand for :x=>y. That is: a hash with one element, that
has as key *symbol* :x, and as value whatever is in variable y. In the
second case, the key of the hash is whatever you have currently in
variable x.

If you have this short script:

--8<----8<----8<----8<--
def m(h)
pp h
pp h.class
pp h.keys[0]
pp h.keys[0].class
end

x=1
y=2

m(x=>y)
print("\n")
m(x:y)
--8<----8<----8<----8<--

and run it, you obtain

{1=>2}
Hash
1
Integer

{:x=>2}
Hash
:x
Symbol

HTH

Carlo

--
* Se la Strada e la sua Virtu' non fossero state messe da parte,
* K * Carlo E. Prelz - fluido@fluido.as che bisogno ci sarebbe
* di parlare tanto di amore e di rettitudine? (Chuang-Tzu)
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4

def tt (x=123)
  puts x
end

=> :tt

tt

123
=> nil

tt(456)

456
=> nil

The code above is the default argument I know.

But this one,

def tt2 (x:123)
  puts x

1> end
=> :tt2

tt2

123
=> nil

tt2(456)

Traceback (most recent call last):
        5: from /usr/bin/irb:23:in `<main>'
        4: from /usr/bin/irb:23:in `load'
        3: from /Library/Ruby/Gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        2: from (irb):10
        1: from (irb):6:in `tt2'
ArgumentError (wrong number of arguments (given 1, expected 0))

As you see it fails.
But the following calling could work.

tt2(x:456)

456
=> nil

tt2(:x=>456)

456
=> nil

what's the trick behind it?

Thanks & regards,
Henry

···

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5

"x" in tt2 is a keyword argument:

https://docs.ruby-lang.org/en/3.0/syntax/methods_rdoc.html#label-Keyword+Arguments

···

On December 18, 2022 1:09:51 AM UTC, Henry R via ruby-talk <ruby-talk@ml.ruby-lang.org> wrote:

def tt2 (x:123)
  puts x
end

tt2

123

tt2(456)

ArgumentError (wrong number of arguments (given 1, expected 0))

tt2(x:456)

456

tt2(:x=>456)

456

what's the trick behind it?

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