# Hash as paramerter container

**URL:** <https://www.ruby-forum.com/t/hash-as-paramerter-container/51939>\
**Category:** Ruby\
**Created:** [January 9, 2006, 2:54pm UTC](https://www.ruby-forum.com/t/hash-as-paramerter-container/51939 "2006-01-09T14:54:06Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![SchSSS\_le\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/a183cd/32.png) [@SchSSS\_le\_Daniel](https://www.ruby-forum.com/u/SchSSS_le_Daniel)\
**Post date:** [January 9, 2006, 2:54pm UTC](https://www.ruby-forum.com/t/hash-as-paramerter-container/51939/1 "2006-01-09T14:54:06Z")

</div>

Hello all,

I am looking for Ruby equivalent for this Python Code

> > > def foo(a,b,c):  
> > > … print "a is ", a  
> > > … print "b is ", b  
> > > … print "c is ", c  
> > > …
> 
> > > h = {“c”:3, “a”:1, “b”:2}
> > > 
> > > foo  
> > > \<function foo at 0x403d6f7c\>
> 
> > > foo(\*\*h)  
> > > a is 1  
> > > b is 2  
> > > c is 3

my first try

=\> {“c”=\>333, :b=\>2, :a=\>1}  
irb(main):017:0\> def foo a,b,c  
irb(main):018:1\> puts “a is #{a}”  
irb(main):019:1\> puts “b is #{b}”  
irb(main):020:1\> puts “c is #{c}”  
irb(main):021:1\> end  
=\> nil  
irb(main):022:0\> foo \*h  
a is c333  
b is b2  
c is a1  
=\> nil

this seem to replace (or substituate) the parameters expected by foo  
in the order of hash. And since hash has no order (in both languages)  
it’s a random replacement.

Is there a trick I don’t know about?

Regards, Daniel

ps:

The case of unpacking an array seem to be 1:1 mapping betweeen Python  
and Ruby.

> > > n = [1,2,3]
> > > 
> > > def bar(\*args):  
> > > … for i in args:  
> > > … print i  
> > > …
> 
> > > bar(\*n)  
> > > 1  
> > > 2  
> > > 3
> 
> > > bar(1,2,3)  
> > > 1  
> > > 2  
> > > 3
> 
> > >

irb(main):065:0\> def bar \*args  
irb(main):066:1\> args.each {|i| puts i}  
irb(main):067:1\> end  
=\> nil  
irb(main):068:0\> n = [1,2,3]  
=\> [1, 2, 3]  
irb(main):069:0\> bar(\*n)  
1  
2  
3  
=\> [1, 2, 3]  
irb(main):070:0\> bar(1,2,3)  
1  
2  
3  
=\> [1, 2, 3]  
irb(main):071:0\>

---

<div class="post-metadata">

**Author:** ![SchSSS\_le\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/a183cd/32.png) [@SchSSS\_le\_Daniel](https://www.ruby-forum.com/u/SchSSS_le_Daniel)\
**Post date:** [January 9, 2006, 3:05pm UTC](https://www.ruby-forum.com/t/hash-as-paramerter-container/51939/2 "2006-01-09T15:05:38Z")

</div>

On Jan 9, 2006, at 7:53 AM, Schüle Daniel wrote:

> > > > foo  
> > > > \<function foo at 0x403d6f7c\>
> > 
> > > > foo(\*\*h)  
> > > > a is 1  
> > > > b is 2  
> > > > c is 3

Here are some ideas:

> > def show( a, b, c)  
> > puts “a is #{a}”  
> > puts “b is #{b}”  
> > puts “c is #{c}”  
> > end  
> > =\> nil
> 
> > params = {:a =\> 1, :b =\> 2, :c =\> 3}  
> > =\> {:b=\>2, :c=\>3, :a=\>1}
> 
> > show(\*params.values\_at(:a, :b, :c))  
> > a is 1  
> > b is 2  
> > c is 3  
> > =\> nil

That’s about the closet I can get what what you posted, I think.

> > def show( args )  
> > [:a, :b, :b].each { |key| puts “#{key} is #{args[key]}” }  
> > end  
> > =\> nil
> 
> > show(:a =\> 1, :b =\> 2, :c =\> 3)  
> > a is 1  
> > b is 2  
> > b is 2  
> > =\> [:a, :b, :b]

This one is more Rubyish though, to me. It uses Ruby’s almost named  
parameter syntax.

Hope that gives you some new ideas.

James Edward G. II

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<div class="post-metadata">

**Author:** ![SchSSS\_le\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/a183cd/32.png) [@SchSSS\_le\_Daniel](https://www.ruby-forum.com/u/SchSSS_le_Daniel)\
**Post date:** [January 9, 2006, 6:37pm UTC](https://www.ruby-forum.com/t/hash-as-paramerter-container/51939/3 "2006-01-09T18:37:53Z")

</div>

What about

irb(main):033:0\> h = {:c=\>333,:b=\>2, :a=\>1}  
=\> {:c=\>333, :a=\>1, :b=\>2}  
irb(main):034:0\> def foo h  
irb(main):035:1\> puts “a is #{h[:a]}”  
irb(main):036:1\> puts “b is #{h[:b]}”  
irb(main):037:1\> puts “c is #{h[:c]}”  
irb(main):038:1\> end  
=\> nil  
irb(main):039:0\> foo h  
a is 1  
b is 2  
c is 333  
=\> nil

---

<div class="post-metadata">

**Author:** ![SchSSS\_le\_Daniel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/a183cd/32.png) [@SchSSS\_le\_Daniel](https://www.ruby-forum.com/u/SchSSS_le_Daniel)\
**Post date:** [January 9, 2006, 5:58pm UTC](https://www.ruby-forum.com/t/hash-as-paramerter-container/51939/4 "2006-01-09T17:58:30Z")

</div>

Schüle Daniel wrote:

> > > >
> 
> irb(main):017:0\> def foo a,b,c
> 
> this seem to replace (or substituate) the parameters expected by foo  
> in the order of hash. And since hash has no order (in both languages)  
> it’s a random replacement.
> 
> Is there a trick I don’t know about?

I don’t know Python but I assume that foo(\*\*h) assigns hash entries to  
function arguments. Ruby cannot do this because parameter names are  
lost  
at runtime. Here’s what you can do:

def foo(\*a)  
case a.length  
when 1  
a[0].each {|k,v| puts “#{k} is #{v}”}  
when 3  
puts “a is #{a[0]}”  
puts “b is #{a[1]}”  
puts “c is #{a[2]}”  
else  
raise ArgumentError, “wrong number of arguments”  
end  
end

> > foo(1,2,3)  
> > a is 1  
> > b is 2  
> > c is 3  
> > =\> nil
> 
> > foo(:x=\>1, :y=\>32, :z=\>4)  
> > y is 32  
> > z is 4  
> > x is 1  
> > =\> {:y=\>32, :z=\>4, :x=\>1}
> 
> > foo(1,2,3,4)  
> > RuntimeError: Illegal Call  
> > from (irb):24:in `foo’  
> > from (irb):29  
> > from :0

But generally you would decide whether you use a hash or individual  
parameters. You could go through some hoops to retrofit something on  
Ruby  
that will behave approximately like Python does but I won’t be fast or  
elegant and I guess there would be some limitations. But Ruby 2 is will  
introduce new functionality here (named parameters / arguments); it  
might  
then be possible to do what you know from Python.

HTH

Kind regards

```
robert
```