[Q] case based on object class

[George Moschovitis]

Hello everyone,

I wonder if there is a more elegant/efficient way to rewrite
the case structure in the following code snippet:

def myfunc(obj)
case obj.class.name
when Fixnum.name
puts :Fixnum
when Float.name
puts :Float
...
default
puts :Object
end
end

thanks in advance,

George Moschovitis


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[Michael Neumann]

Hello everyone,

I wonder if there is a more elegant/efficient way to rewrite
the case structure in the following code snippet:

def myfunc(obj)
case obj.class.name
when Fixnum.name
puts :Fixnum
when Float.name
puts :Float
...
default
puts :Object
end
end

case obj
when Fixnum
puts obj.class.to_s.to_sym
when Float
...
else
puts :Object
end


Regards,

Michael

 

[Hal Fulton]

Hello everyone,

I wonder if there is a more elegant/efficient way to rewrite
the case structure in the following code snippet:

Certainly... see below.

def myfunc(obj)
case obj
when Fixnum
puts :Fixnum
when Float
puts :Float
...
default
puts :Object
end
end

This works because case invokes ===, which takes a minute
or three to understand.


Hal

PS - In my Mozilla, your font is microscopic. :0


H

 

[George Moschovitis]

This works because case invokes ===, which takes a minute

or three to understand.

Thank you Hal and Michael!

Ruby can be VERY surprising after all. After the initial shock it
feels natural though.

-g.

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[George Moschovitis]

Hmm my example was wrong, what I wanted to write is:

def myfunc(klass)
case klass.name
when Fixnum.name
puts :Fixnum
when Float.name
puts :Float
...
default
puts :Object
end
end

myfunc(obj.class)

Now this === doesnt work I am sure the solution is obvious,
but I would appreciate some help.

regards,
George Moschovitis


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the contents of this message. The full corporate policy is available on
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[Hal Fulton]

Hmm my example was wrong, what I wanted to write is:

def myfunc(klass)
case klass.name
when Fixnum.name
puts :Fixnum
when Float.name
puts :Float
...
default
puts :Object
end
end

myfunc(obj.class)

Now this === doesnt work I am sure the solution is obvious,
but I would appreciate some help.

I am not sure what you want to do... do you want to separate these
things by class and print out the corresponding symbol?

Anyhow, I tried your code and it worked fine for me. I substituted
4 for obj and commented the ... of course.

What's the problem about?


Hal

 

[Hal Fulton]

Anyhow, I tried your code and it worked fine for me. I substituted
4 for obj and commented the ... of course.

Also, what's this 'default' thing? I'm surprised it didn't give a
syntax error... 'else' is the thing.

I guess it's interpreting that as a method call but you're never
reaching it.


Hal

 

[George Moschovitis]

I am not sure what you want to do... do you want to separate these

things by class and print out the corresponding symbol?

i want to execute different code depending on the klass (Class) object
given to the method.

Anyhow, I tried your code and it worked fine for me. I substituted
4 for obj and commented the ... of course.

the code works, I am wondering if there is a more elegant/efficient
way to write it.

-g.

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[George Moschovitis]

Also, what's this 'default' thing? I'm surprised it didn't give a

hmm that was an error, I thought I was writing C or something.
it was pseudocode anyway, just to illustrate my question...

-g.

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[Hal Fulton]

the code works, I am wondering if there is a more elegant/efficient
way to write it.

Well, I'd wonder why you're testing the class instead of the
object.

def myfunc(obj)
case obj
when Fixnum
# ...
when Float
# ...
else
# ...
end
end


myfunc(some_obj)


This seems better to me...


Hal

 

[trans. (T. Onoma)]

On Monday 11 October 2004 06:04 am, George Moschovitis wrote:| def myfunc(klass)|          case klass.name|                  when Fixnum.name|                          puts :Fixnum|                  when Float.name|                          puts :Float|                  ...|                  default|                          puts :Object|          end| end
This doesn't work?
def myfunc(klass)     case klass             when Fixnum                  puts :Fixnum              when Float                 puts :Float              ...             default                 puts :Object          end end

BTW the method being used by case in the above is Class#===, to be more exact it is calling Fixnum#=== and Float#===
T.

 

[Martin DeMello]

How about

case klass.name.to_sym
when :Fixnum
...

martin

 

[Robert Klemme]

i want to execute different code depending on the klass (Class) object
given to the method.


the code works, I am wondering if there is a more elegant/efficient
way to write it.

The OO way is to use a mapping IMHO:

ACTION_MAPPING = {
Fixnum => lambda { puts "Fixnum" },
Float => lambda { puts "Float" },
String => lambda { puts "String" },
}

def myfunc(klass)
code = ACTION_MAPPING[klass]
raise ArgumentError, "Klass not found: #{klass}" unless code
code.call
end

You can even define a block for the error as default effectively rendering
the method a one liner like this:

ACTION_MAPPING = Hash.new( lambda { raise ArgumentError, "Klass not
found" } ).update(
Fixnum => lambda { puts "Fixnum" },
Float => lambda { puts "Float" },
String => lambda { puts "String" }
)

def myfunc(klass) ACTION_MAPPING[klass].call end

Kind regards

robert

 

[Robert Klemme]

The OO way is to use a mapping IMHO:

I forgot to mention that this is also more efficient if you have many
classes.

ACTION_MAPPING = {
Fixnum => lambda { puts "Fixnum" },
Float => lambda { puts "Float" },
String => lambda { puts "String" },
}

def myfunc(klass)
code = ACTION_MAPPING[klass]
raise ArgumentError, "Klass not found: #{klass}" unless code
code.call
end

You can even define a block for the error as default effectively rendering
the method a one liner like this:

ACTION_MAPPING = Hash.new( lambda { raise ArgumentError, "Klass not
found" } ).update(
Fixnum => lambda { puts "Fixnum" },
Float => lambda { puts "Float" },
String => lambda { puts "String" }
)

def myfunc(klass) ACTION_MAPPING[klass].call end

And then there is also the option to define those methods as singleton
methods of the classes although I recommend to do this *only* if the
functionality is general enough and has to do with the class more than
with your app.

Kind regards

robert