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comp.lang.ruby

Duck typing bunches of strings

List Recv

3/27/2006 6:36:00 AM

In my quest to master the fine art of duck typing / overloading, I've
run into this probem:

How can I identify a collection?
The problem is: String mixes in Enumerable, although it ain't a
collection.

My method wants to act differently if it's given a collection, then if
it's just given a single object. I would check .respond_to? :each -
but String does, unfortunately.

Currently, I'm forced to do .kind_of? Array - but this ain't duck
typing.

Any ideas? I'd like to separate Array, Hash, Set, etc. etc. from
single member objects.
8 Answers

Daniel Baird

3/27/2006 7:11:00 AM

0

maybe you just want anything that has respond_to? :each and isn't a String.

From memory String doing Enumerable is a bit of a special case; if you
eliminate just String and any of it's subclasses you're probably left with
the "real" Enumerables.

;Daniel


On 27/03/06, listrecv@gmail.com <listrecv@gmail.com> wrote:
>
> In my quest to master the fine art of duck typing / overloading, I've
> run into this probem:
>
> How can I identify a collection?
> The problem is: String mixes in Enumerable, although it ain't a
> collection.
>
> My method wants to act differently if it's given a collection, then if
> it's just given a single object. I would check .respond_to? :each -
> but String does, unfortunately.
>
> Currently, I'm forced to do .kind_of? Array - but this ain't duck
> typing.
>
> Any ideas? I'd like to separate Array, Hash, Set, etc. etc. from
> single member objects.
>
>
>


--
Daniel Baird
http://danie... (TiddlyW;nks! :: Whiteboard Koala :: Blog :: Things
That Suck)
[[My webhost uptime is ~ 92%.. if no answer pls call again later!]]

Jason Hutchens

3/27/2006 10:46:00 AM

0

What's wrong with "object.kind_of?(Enumerable)" and
"class.include?(Enumerable)"?

my_array = Array.new
my_array.kind_of?(Enumerable) # => true
Array.include?(Enumerable) # => true

dblack

3/27/2006 1:00:00 PM

0

List Recv

3/27/2006 3:42:00 PM

0

String is also Enumerable, see OP.

List Recv

3/27/2006 3:43:00 PM

0

That wouldn't be very duckish - I'd still need to explicitly state
which objects are acceptable - the whole point is to leave that up to
the user, as long as the object can do what it needs to, I never need
to hear it's name.

Logan Capaldo

3/27/2006 6:33:00 PM

0


On Mar 27, 2006, at 10:43 AM, listrecv@gmail.com wrote:

> That wouldn't be very duckish - I'd still need to explicitly state
> which objects are acceptable - the whole point is to leave that up to
> the user, as long as the object can do what it needs to, I never need
> to hear it's name.
>
>

Just curious, but what happens if you just throw a string at it?
str.each { |s| } tends to be str most of the time anyway. alternatively:

class Object
def scalar?
true # or possibly not respond_to? :each
end
end

module Enumerable
def scalar?
false
end
end

class String
def scalar?
true
end
end

Thanks to the magic of inheritance it will all work out

Jason Hutchens

3/28/2006 2:49:00 AM

0

> ri Enumerable
The +Enumerable+ mixin provides collection classes with several
traversal and searching methods, and with the ability to sort. The
class must provide a method +each+, which yields successive members
of the collection...

> ri String.each
Splits _str_ using the supplied parameter as the record separator
(+$/+ by default), passing each substring in turn to the supplied
block.

Okay, so maybe String shouldn't mixin Enumerable in the first place.

Mark T

3/28/2006 3:50:00 PM

0

On Tue, 28 Mar 2006 03:33:12 +0900, Logan Capaldo wrote:

> Just curious, but what happens if you just throw a string at it?
> str.each { |s| } tends to be str most of the time anyway.

From the docs:

Splits _str_ using the supplied parameter as the record separator
(+$/+ by default), passing each substring in turn to the supplied
block. If a zero-length record separator is supplied, the string is
split on +\n+ characters, except that multiple successive newlines
are appended together.

String#each is actually the same as String#each_line (one is aliased to
the other).


To the OP: why do you want to exclude String? Shouldn't you allow your
user to consider a string as a collection of lines? That way, someone
using your library to work on data from a newline-separated file doesn't
have to parse it themselves, just load it into a String and call your
method on it.



Mark T