Greetings!
I am wondering why there are two separate classes (TrueClass and
FalseClass) to deal with boolean types insead of one class (something
like Boolean?). Do you know
why the library designer desided to use this approach?
Your help will be greatly apreciated.
Thanks
On Mar 30, 2006, at 1:31 PM, PrimaryKey wrote:
Greetings!
I am wondering why there are two separate classes (TrueClass and
FalseClass) to deal with boolean types insead of one class (something
like Boolean?). Do you know
why the library designer desided to use this approach?Your help will be greatly apreciated.
This has been discussed many, many times before. Here’s a reading list:
http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb?key=TrueClass
+FalseClass&cginame=namazu.rb&submit=Search&dbname=ruby-
talk&max=50&whence=0
–
Eric H. - [email protected] - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant
Since everything in ruby is an object, there need to be objects for
representing true and false. Once you have those, why do you need a
Boolean class?
PrimaryKey wrote:
I am wondering why there are two separate classes (TrueClass and
FalseClass) to deal with boolean types insead of one class (something
like Boolean?). Do you know
why the library designer desided to use this approach?
I think it is because true and false don’t really have anything in
common in Ruby. No way to share code.
You can always fix it pretty easily:
module Boolean; end
[true, false].each do |obj|
obj.extend(Boolean)
end
true.is_a?(Boolean) # => true
false.is_a?(Boolean) # => true
But note that in Ruby all objects (except false and nil) can be used as
true values. And they are used for just that even in the standard
library.
On Mar 31, 2006, at 9:27 AM, Christian N. wrote:
case y
when Integer
when Boolean
end
case y
when Integer
when TrueClass,FalseClass
end
works ok, right? I kind of wish the class names were just True and
False.
Gary W.
“[email protected]” [email protected] writes:
Since everything in ruby is an object, there need to be objects for
representing true and false. Once you have those, why do you need a
Boolean class?
if a.kind_of? Boolean
case y
when Integer
when Boolean
end
I often wanted this shortcut…
On Fri, 31 Mar 2006, Christian N. wrote:
when Boolean
endI often wanted this shortcut…
indeed. i tend to use
case obj
when Klass
when TrueClass, FalseClass
end
which is ugly.
another thing a real Boolean class could give is a ‘maybe’ obj such that
maybe or true -> maybe
maybe or true and false or true -> maybe
maybe and false -> maybe
although i can’t think of anything attm to do with this it would
undoubtably
lead to some nice logical constructs that more closely parallel the way
we
think.
i’ve brought this up once or twice before - maybe we should just put
together
a patch and send to ruby-core?
regards.
-a
[email protected] wrote:
On Fri, 31 Mar 2006, Christian N. wrote:
if a.kind_of? Boolean
case y
when Integer
when Boolean
end
What kind of scenarios would you want to use such a construct? It seems
to me not very rubyish to be switching based on the class of an object.
As I understand it, the more conventional way to deal with potentially
diverse argument types is to use the respond_to? method. This keeps the
door open for duck typing.
another thing a real Boolean class could give is a ‘maybe’ obj such that
…
although i can’t think of anything attm to do with this it would undoubtably
lead to some nice logical constructs that more closely parallel the way we
think.
It sounds like you’re talking about a sort of restricted fuzzy logic,
which is very cool, but is not appropriate for the core of a general
purpose language. Considering that every expression can be interpreted
in a boolean context, what would a maybe value do? Either behavior
seems wrong.
“[email protected]” [email protected] writes:
to me not very rubyish to be switching based on the class of an object.
As I understand it, the more conventional way to deal with potentially
diverse argument types is to use the respond_to? method. This keeps the
door open for duck typing.
Except we don’t have a to_bool, either ;-).
Still, I can saw enough cases where I wanted such a “case”, and
grumbly used TrueClass,FalseClass.
On Sat, 1 Apr 2006, [email protected] wrote:
me not very rubyish to be switching based on the class of an object. As I
understand it, the more conventional way to deal with potentially diverse
argument types is to use the respond_to? method. This keeps the door open
for duck typing.
i generally do use duck typing, but sometimes it is simply not
appropriate or
become too verbose. for example, consider a matrix class with the
following
behaviour
1d
m[true] #=> all data returned
m[] #=> all data returned
m[true] = elems #=> data along all dims set
m[] = elems #=> data along all dims set
m[int] #=> treat as 1d array, return elem
m[int] = elem #=> treat as 1d array, set idx to elem
m[off, len] #=> treat as 1d array, return elems off thru
len
m[off, len] = elem #=> treat as 1d array, set elems off thru len
to elem
m[a … b] #=> treat as 1d array, return elems in range
m[a … b] = elem #=> treat as 1d array, set elems in range to
elem
m[n] #=> idx one matrix by another
2d
generalize all above so multiple indices access in
multi-dimensional
fashion. eg
m[0,1,2] #= return idx x,y,z
m[0,30..42,true] #= return column 0, rows 30 to 42, in all height
dims
now, in case you are thinking that i’m just being difficult, this is
exactly
how the narray class works
http://narray.rubyforge.org/SPEC.en
have fun writing that with respond_to? !! 
also, when working with concrete data structures (like binary output
from C
programs) it’s often quite sufficient to have a type mapping. further
more
it’s sometimes critical, for instace writing the word located at
offset=42,
len=4 with a packed int value or sending a given sequence of bytes down
a
socket that a given type is used and it’s much more natural to write
def send buf, which = nil
case which
when Fixnum
socket.write [which].pack(‘N’)
socket.write buf
when NilClass
socket.write [buf.size].pack(‘N’)
socket.write buf
when Range
length = which.last - which.first
socket.write [length].pack(‘N’)
socket.write buf[which]
else
raise TypeError, which.class
end
end
than something using respond_to?.
don’t get me wrong - i defintely advocate duck typing, but when the
number of
possible input types becomes large and behaviour is different depending
on
that type it becomes cumbersome. this is the price we pay for not
having c–
style polymorphism. in fact, it’s very common to see the two styles
combined:
case arg
when Fixnum
…
when Range
…
else # dunno - assume String and use in a duck type fashion
end
context, what would a maybe value do? Either behavior seems wrong.
i disagree - ruby (and hardware) already supports this style of logic in
several ways:
harp:~ > irb
irb(main):001:0> nan = 0.0/0.0
=> NaN
irb(main):002:0> nan * 42
=> NaN
irb(main):003:0> nan * 42 + 42.0
=> NaN
irb(main):004:0> obj = Object.new and obj.taint
=> #Object:0xb75a5fac
irb(main):005:0> (obj.to_s << “string”).tainted?
=> true
irb(main):006:0> (“string” << obj.to_s).tainted?
=> true
there’s no good reason, imho, why this style of logical behaviour could
not be
part of the logical classes (TrueClass/FalseClass) and operators (and,
or,
not).
regards.
-a
On Sat, Apr 01, 2006 at 12:38:43AM +0900, [email protected] wrote:
} [email protected] wrote:
} > On Fri, 31 Mar 2006, Christian N. wrote:
} > > if a.kind_of? Boolean
} > >
} > > case y
} > > when Integer
} > > when Boolean
} > > end
}
} What kind of scenarios would you want to use such a construct? It
seems
} to me not very rubyish to be switching based on the class of an
object.
} As I understand it, the more conventional way to deal with potentially
} diverse argument types is to use the respond_to? method. This keeps
the
} door open for duck typing.
[…]
The most obvious answer is that it is needed for various kinds of
serialization. I wrote something like this just the other day. I needed
to
do XML-RPC serialization (yes, I know there is XML-RPC support in the
standard library, but I needed something slightly different that was
easier
to do by hand), so I needed to know what kind of value I was
serializing.
–Greg
unknown wrote:
maybe or true -> maybe
Wouldn’t maybe or true be true?
–
– Jim W.
[email protected] wrote:
end
You could always assign some new constants to them:
True = TrueClass
False = FalseClass
case y
when Integer
when True, False
end
John W. Long wrote:
You could always assign some new constants to them:
True = TrueClass
False = FalseClasscase y
when Integer
when True, False
end
Or just use the literal constants, that already exist:
case y
when Integer
when true, false
end
On Mar 31, 2006, at 10:21 AM, [email protected] wrote:
maybe and false -> maybe
Shouldn’t this be false?
{true, false} and false is going to be false regardless of what
maybe is
On Mar 31, 2006, at 5:00 PM, Florian F. wrote:
Or just use the literal constants, that already exist:
case y
when Integer
when true, false
end
Another example where the Ruby ‘does the right thing’.
Thanks for the reminder.
Gary W.
another thing a real Boolean class could give is a ‘maybe’ obj such that
maybe or true -> maybe maybe or true and false or true -> maybe maybe and false -> maybe
What whould this do
print "hello" if maybe
or this
while maybe
print "hello"
end
// Niklas
[email protected] wrote:
def maybe() [rand].pack(‘f’).unpack(‘c’).first[0].zero? end
What does
[rand].pack(‘f’).unpack(‘c’).first[0]
do that
rand(2)
doesn’t?
On Sun, 2 Apr 2006, Joel VanderWerf wrote:
doesn’t?
sheesh - can’t you tell it looks longer!
-a
On Apr 1, 2006, at 10:03 AM, [email protected] wrote:
number and look at the last bit for instance, 0 -> false, 1 -> true.
- h.h. the 14th dali lama
As if my code wasn’t already non-deterministic
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