Truth value evaluating of an object

[Dave River]

I know ruby treat an object as false whenever it is nil or false.
However, I wonder if there are any other ways to change this behavior.

For example, I define a class called AreYouOk.
class AreYouOk
def initialize(ok)
@ok = ok
end
end

x = AreYouOk.new(false)
puts "you are ok" if x

Since x is not nil, ruby prints " you are ok".
However, I want ruby to make the decision based on the @ok instance
variable. Are there any ways to do that?

I know that there is a method called __bool__ in Python. You can define
your __bool__ method in your class. The truth value of an object is
based on the return value of __bool__. Does ruby provide similar
mechanism?

 

[Dave River]

Thus 'if x.ok?' returns the same as 'if x' for any object, but @ok for
yours!

Thanks for your explanation!

In fact, I am making a wrapper class called Boolean which cooperates
with some legacy code in my company because there are some compatibility
problems between different languages.

I write some code like the following and the Boolean object hides some
underlying code which solve the compatibility problems.
x = Boolean.new()
if x
do something....
end

If ruby does not support something like __bool__ in Python, I need to
write some code in the following way.
x = Boolean.new()
if x.evaluate()
do something...
end

But I would prefer "if x " instead of "if x.evaluate" because it is more
straight forward. So, I would like to know whether there are any ways to
do so.

Regards,
Dave

 

[Phrogz]

I write some code like the following and the Boolean object hides some
underlying code which solve the compatibility problems.
x = Boolean.new()
if x
do something....
end

If ruby does not support something like __bool__ in Python, I need to
write some code in the following way.
x = Boolean.new()
if x.evaluate()
do something...
end

But I would prefer "if x " instead of "if x.evaluate" because it is more
straight forward. So, I would like to know whether there are any ways to
do so.

There are not any ways to do so in Ruby. Sorry. (This question comes
up every few weeks or so.)

 

[Robert Klemme]

Thanks for your explanation!

In fact, I am making a wrapper class called Boolean which cooperates
with some legacy code in my company because there are some compatibility
problems between different languages.

I write some code like the following and the Boolean object hides some
underlying code which solve the compatibility problems.
x = Boolean.new()
if x
do something....
end

If ruby does not support something like __bool__ in Python, I need to
write some code in the following way.
x = Boolean.new()
if x.evaluate()
do something...
end

But I would prefer "if x " instead of "if x.evaluate" because it is more
straight forward. So, I would like to know whether there are any ways to
do so.

What exactly does Boolean do? Maybe you can get rid of it or do some
other changes so you can directly work with "true" and "false.

Kind regards

robert

 

[Morton Goldberg]

I know ruby treat an object as false whenever it is nil or false.
However, I wonder if there are any other ways to change this behavior.

For example, I define a class called AreYouOk.
class AreYouOk
def initialize(ok)
@ok = ok
end
end

x = AreYouOk.new(false)
puts "you are ok" if x

Since x is not nil, ruby prints " you are ok".
However, I want ruby to make the decision based on the @ok instance
variable. Are there any ways to do that?

I know that there is a method called __bool__ in Python. You can
define
your __bool__ method in your class. The truth value of an object is
based on the return value of __bool__. Does ruby provide similar
mechanism?

What you are asking about looks to me like a flag class.

<code>
class Flag
def initialize(state=false)
@state = state
end
def set?
@state
end
def set
@state = true
end
def clear
@state = false
end
end

ok = Flag.new
puts "you are ok" if ok.set?
puts "you are not ok" unless ok.set?
ok.set
puts "you are ok" if ok.set?
puts "you are not ok" unless ok.set?

</code>

First the string "you are not ok" is printed. After the flag is set,
the string "you are ok" is printed.

Regards, Morton