From: Joseph McDonald <joe@...>
Date: 2001-05-15T11:21:46+09:00
Subject: [ruby-talk:15135] specifying argument type to method?


Hi,

I'd like to specify that a method accepts it's argument as a specified
type.  How can I do this?

Here is the problem:  I want to pass in name-based arguments to the
method fetch(), sometimes I need to send in 2 arguments that have
the same name, i.e:

fetch('create_time' => ['<', 112341234],'create_time' => ['>', 112111234],
'other' => 'a')

It doesn't help to do things  like:

def fetch(args=[]) or:
def fetch(*args)

The first one reads in the args as a hash unless you don't pass
any, in which  case you get an empty array.

The second one simply assigns the keyword hash as the first
element of the args array.

So, I can't think of a way to pass multiple values for the same keyword
without making the keyword value an array, like:

fetch('create_time' => [ ['<', 123412341], ['>', 111121234] ])
But that is not very readable. :(

So, how to "cast" the type that fetch gets?  If that was possible, I could
make it some homegrown type that is a hash, but converts the values to
arrays
if more than 1 instance of a key is detected.

Also, I ran into something weird when investigating this:

I thought this would work, but it didn't.  Also, Of course I wouldn't
reccomend changing Hash... just wanted to see if it would work.  The
idea is if we could associate this type of hash with the args to fetch...
Weird thing is that it didn't work, and I don't know why.  It almost seems
like there are 2 versions of Hash running around in the program.

# an array hash... if a key already exists, make it's value an array.
class Hash
  alias oldset []=

  def []=(k,v)
    if self[k]
      arr = []
      arr << self[k] << v
      oldset k, arr
    else
      oldset k, v
    end
  end
end

def fetch(args)
  p args
  p args.type
end

fetch("create_time" => ['<', 112341234], "create_time" => ['>', 112111235],
"other" => "joe")

m = Hash.new
m["joe"] = 123
p m
m["joe"] = 456
p m
m["tom"] = 890
p m

Output:
{"create_time"=>[">", 112111235], "other"=>"joe"}
Hash
{"joe"=>123}
{"joe"=>[123, 456]}
{"joe"=>[123, 456], "tom"=>890}

weird huh?

thanks,
-joe