How can I overload a method in Ruby

Ruby
1

This is my class definition:
class Impl
include MyModule
def fun()
puts (“fun”)
end

def fun(directory)
puts (“fun directory”)
end
end
m=Impl.new()
m.fun()

When I run this program, I got this error:

class_objects/module.rb:22:in `fun’: wrong number of arguments (0 for 1)
(ArgumentError)
from class_objects/module.rb:22

I declared two methods with the same name but different parameters. Why
can’t ruby support overload method?

2

On Nov 16, 2008, at 23:26 , Zhao Yi wrote:

short answer: you can’t (via normal ruby).

When I run this program, I got this error:

class_objects/module.rb:22:in `fun’: wrong number of arguments (0
for 1)
(ArgumentError)
from class_objects/module.rb:22

I declared two methods with the same name but different parameters.
Why
can’t ruby support overload method?

because it wasn’t designed to, that’s why.

You can use default args to do what you want above:

3

there is no overloading, only overriding.

You can have variable number of arguments by writing

def fun(*params)
#here params is an array of your arguments, [] if none.
end

you can also have a default value for your parameter:

class Impl
include MyModule

def fun(directory = “”)
puts “fun #{directory}”
end

end
m=Impl.new()
m.fun()

>> fun

m.fun “/dev/null”

>> fun /dev/null"

4

Ryan D. wrote:

On Nov 16, 2008, at 23:26 , Zhao Yi wrote:

short answer: you can’t (via normal ruby).

When I run this program, I got this error:

class_objects/module.rb:22:in `fun’: wrong number of arguments (0
for 1)
(ArgumentError)
from class_objects/module.rb:22

I declared two methods with the same name but different parameters.
Why
can’t ruby support overload method?

because it wasn’t designed to, that’s why.

You can use default args to do what you want above:

I am new to Ruby. What’s do you mean by default args?
thanks

5

Einar Magnús Boson wrote:

there is no overloading, only overriding.

You can have variable number of arguments by writing

def fun(*params)
#here params is an array of your arguments, [] if none.
end

you can also have a default value for your parameter:

class Impl
include MyModule

def fun(directory = “”)
puts “fun #{directory}”
end

end
m=Impl.new()
m.fun()

>> fun

m.fun “/dev/null”

>> fun /dev/null"

ok I understand. Just curious, overload is a good feature in OO
programming. Why doesn’t Ruby support it? If I use the method you
mentioned, I have to check the parameters and use if - else or swith to
distinguish them.

6

From: Zhao Yi [mailto:[email protected]]

ok I understand. Just curious, overload is a good feature in OO

programming. Why doesn’t Ruby support it? If I use the method you

mentioned, I have to check the parameters and use if - else

or swith to distinguish them.

maybe because of the ff dilemma:

def m(1)
end

def m(“one”)
end

ruby will be forced to check type… wc leads to static typing… wc is
not matz ruby…

btw, Zhao, can you give us a real case where you really need to do
method loading?

kind regards -botp

7

I find that overriding is much more powerful. You can override just
about any method.
Try

class Fixnum
def to_s
“this is kinda stupid”
end
end

puts 5

Overloading is mostly used for default arguments anyways isn’t it? and
also requires static typing I think.

Einar Magnús Boson
+354-661 1649
[email protected]
[email protected]

8

Peña, Botp wrote:

From: Zhao Yi [mailto:[email protected]]

ok I understand. Just curious, overload is a good feature in OO

programming. Why doesn’t Ruby support it? If I use the method you

mentioned, I have to check the parameters and use if - else

or swith to distinguish them.

maybe because of the ff dilemma:

def m(1)
end

def m(“one”)
end

ruby will be forced to check type… wc leads to static typing… wc is
not matz ruby…

btw, Zhao, can you give us a real case where you really need to do
method loading?

kind regards -botp

I want to write a build method which will build source code in a
directory. I assume there are two build methods, one doesn’t have
parameter while the other have one parameter. The method without
parameter will build the source code in default directory, the method
with one parameter will build the source code in the directory which is
specified by this parameter. With method overloading, I can write them
as below:

def build()
make
end

def build(directory)
cd directory
make
end

but without overloading, I have to do this:
def build(directory)
if(directory == nil)
make
else
cd directory
make
endif
end

9

From: Zhao Yi [mailto:[email protected]]

def build()

make

end

def build(directory)

cd directory

make

end

but without overloading, I have to do this:

def build(directory)

if(directory == nil)

make

else

cd directory

make

endif

end

try it like,

def build directory=nil
cd directory unless directory.nil?
make
end

10

I am a Java developer and new to Ruby. I think I really need some time
to familiar with Ruby.

Anyway, thanks all of your kindly reply.

Yi

11

On Nov 17, 2:26 am, Zhao Yi [email protected] wrote:

end
can’t ruby support overload method?
Although it is not the “Ruby Way” so to speak, Ruby is flexible enough
to allow for ways to do it. For instance:

require ‘facets/overload’

class X
def x
“hello”
end

overload :x, Integer do |i|
  i
end

overload :x, String, String do |s1, s2|
  [s1, s2]
end

end

12

From: Peña, Botp [mailto:[email protected]]

def build directory=nil

cd directory unless directory.nil?

make

end

or if you do not like the if/unless part,

def build directory=“.”
cd directory
make
end

13

Zhao Yi [email protected] writes:

end

def build(directory)
cd directory
make
end

Call it: buildWithDirectory(directory)

but without overloading, I have to do this:
def build(directory)
if(directory == nil)
make
else
cd directory
make
endif
end

If you insist on one name for both, then:

def build(directory=nil)
…
end

so you can call it as build() or build(dir).

14

[email protected] (Pascal J. Bourguignon) writes:

make

end

def build(directory)
cd directory
make
end

Call it: buildWithDirectory(directory)

build_with_directory would probably be a more conventional Ruby function
name.

15

It’s interesting that without the feature of overloading the code is
both shorter and more readable.

16

James C. [email protected] writes:

In this case, this would be more Ruby-idiomatic:

def build(directory = nil)
cd directory if directory
make
end

Yes, Pascal already provided a version with default arg values in the
parent.

17

2008/11/17 Brian A. [email protected]

build_with_directory would probably be a more conventional Ruby function
name.

In this case, this would be more Ruby-idiomatic:

def build(directory = nil)
cd directory if directory
make
end

18

Trans wrote:

Hmm… I suppose that would require Ruby a bit more like Duby?

http://blog.headius.com/2008/03/duby-type-inferred-ruby-like-jvm.html

T.

I know this will not work in every case, but can’t you check the type of
input in a function like foo(x) and convert it to the desired form or
perform the required operation? I agree that this adds more code, and
probably more places for errors, but it places all the code for foo in
one place. I used this when making my own version of rational(). It
would accept one or two integers, floats, strings, or rational numbers,
or combination of them. I only had to change initialize without having
to copy all the other code to methods like rational_f(), rational_i(),
etc.

19

On Nov 17, 2:22 pm, Joe Wölfel [email protected] wrote:

It’s interesting that without the feature of overloading the code is
both shorter and more readable.

Well, default arguments are a different matter really. That’s all that
is needed in this example case, fair enough. But in more complex cases
overloading can be advantageous because it allows for code to be split
up into smaller, more manageable chunks. But Ruby would probably need
to support it internally for the feature to be especially beneficial.
Hmm… I suppose that would require Ruby a bit more like Duby?

http://blog.headius.com/2008/03/duby-type-inferred-ruby-like-jvm.html

T.