Class returns value without method or attribute

If I have a class how do I get it to return a value without specifying a
method or attribute:

class Money
attr_writer :value
end

money = Money.new(5)

money.value => 5

but what if I want:

money => 5

So the actual object returns a value instead of a method or attribute,
like the base classes do.

Many thanks, K.

You could overload the methods you require. For instance if you want
to be able to add two Money objects togeter and get a Money object as
the result using the expression ‘money1 + money2’ you could do

class Money
attr_accessor :value
def+(other)
Money.new(@value + other.value)
end
def initialize(value)
@value = value
end
end
=> nil

m1 = Money.new(5)
=> #<Money:0x2dbb018 @value=5>

m2 = Money.new(10)
=> #<Money:0x2db9098 @value=10>

m1 + m2
=> #<Money:0x2db17d8 @value=15>

Farrel

If I have a class how do I get it to return a value without specifying a
method or attribute:

You want to overload the inspect method:

class Money
attr_accessor :value

def initialize(value)
@value = value
end

def inspect
@value
end

end

irb(main):001:0> require ‘money’
=> true
irb(main):002:0> money = Money.new(5)
=> 5
irb(main):003:0> money
=> 5

Hi,

Here is my approach (similar, but longer):

$ cat money.rb

class Money
attr_accessor :value

def initialize(value)
@value = value
end

def to_s
@value.to_s
end

def +(other)
case other
when Money:
Money.new(@value + other.value)
when Numeric:
Money.new(@value + other)
else
raise “Money can be added to Money or Numeric”
end
end
end

irb(main):002:0> money = Money.new 5
=> #<Money:0x2ba41c8 @value=5>
irb(main):004:0> puts money
5
irb(main):005:0> puts money + money
10
irb(main):006:0> puts money + 100
105
irb(main):007:0> puts money + ‘money’
RuntimeError: Money can be added to Money or Numeric
from ./money.rb:19:in `+’
from (irb):7


Martins

On Fri, 2006-04-28 at 23:39 +0900, kris wrote:

money.value => 5

but what if I want:

money => 5

So the actual object returns a value instead of a method or attribute,
like the base classes do.

Another way to get this kind of behaviour is:

require ‘delegate’
Money = DelegateClass(Float)
m = Money.new(30.0)

p m

30.0
p m + 30.0

60.0
p m + Money.new(30.0)

60.0
p m.class

Money
p m.getobj.class

Float
p m + “notmoney”

2006/4/29, kris [email protected]:

I like the idea of using inspect, will this also allow me to assign
value like:
money = Money.new
money = 5

No, inspect will only affect output with p (or in IRB).

Also do I need to add a method for + and -, is there not a module like
Comparable that I can mixin to get this functionality?

Comparation and arithmetic are two orthogonal concepts, i.e.
completely unrelated. If you want arithmetic in your class, you need
to override +, - and coerce.

http://www.rubygarden.org/ruby?CoerceExplanation
http://www.rubygarden.org/?terms=coerce&submit=SEARCH&handler=searching

For ordering there is mixin Comparable
http://ruby-doc.org/core/classes/Comparable.html
http://www.rubycentral.com/book/ref_m_comparable.html

Are there any other typical methods I should be adding? Excluding the
money specific stuff I have to_s.

to_int is an option, too, if your instance is equivalent to an int.
Additionally you should implement to_i and to_f.

Kind regards

robert

I like the idea of using inspect, will this also allow me to assign
value like:
money = Money.new
money = 5

Also do I need to add a method for + and -, is there not a module like
Comparable that I can mixin to get this functionality?

Are there any other typical methods I should be adding? Excluding the
money specific stuff I have to_s.

Many thanks for all the replies they have been really helpful.

Gordon T. wrote:

If I have a class how do I get it to return a value without specifying a
method or attribute:

You want to overload the inspect method:

class Money
attr_accessor :value

def initialize(value)
@value = value
end

def inspect
@value
end

end

irb(main):001:0> require ‘money’
=> true
irb(main):002:0> money = Money.new(5)
=> 5
irb(main):003:0> money
=> 5

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs