[ruby-talk:01003] Re: a question about to_i

Yukihiro Matsumoto wrote:
> 
> Hi,
> 
> In message "[ruby-talk:00989] a question about to_i"
>     on 99/12/19, Friedrich Dominicus <[e-mail]> writes:
> 
> |Sorry, I'm quite new to ruby. But I encounterd the following problem. If
> |I have a string "bla" and apply to_i to it I get 0. This seems to be
> |quite strange because it is what it is a string so shouldn't an
> |exeception be rissen or s.th simular.
> 
> As Gotoken stated in [ruby-talk:00992], String#to_i (i.e. the to_i
> method of the String class) always return a integer.  This is
> inherited from UNIX's atoi() behavior.

But at least AFAIK there are some checker routines available in ctype.h
things like  isdigit, isascii, isalpha. I don't found s.th simular in
Ruby libs( sorry if I had overseen some points)

> 
> I can prepare exception raising version of the conversion method, but
> we have to decide following:
> 
>   * the name of the method
> 
>     what is the proper name for the exception raising integer
>     conversion method of a string.

I'm too new to ruby to give some good advice on it. But because my
program was "translated" from Python and/or from Scheme and/or from a
small Shell-Skript one might thing that the name for the Python
exception might be a choice.

Here's the python source

def sum_to(add_to,val_to_add):
	old_val = add_to
	try:
		add_to = add_to + int(val_to_add)
		assert add_to == old_val + int(val_to_add), "Adding failed"
	except ValueError:
		pass
	return add_to

As mentioned before I'm to new to Ruby to know if that might work in
Ruby too.

> 
>   * proper behavior
> 
>     on what situation, what kind of exception should be raised?
>     in addition, some may want to retrieve non numeric trailer,
>     the other may want to specify radix.


If there is no number it should fail. If there is a number one might
argue that this part should be turned into an int.

> 
> Let's discuss about it.

What about tests can_be_integer, can_be_float or the like?

If one than would have 
foo = "123"

and call
can_be_integer(foo)

It'll return true than I'm quite safe callint to_i

The question is: Is it worth raising an exception on things that can
happen on normal execution? I'm most of my time an Eiffel Programmer but
I would not use Exceptions on things that I know can fail and this
conversion routines can be applied in many cases so IMO it might be the
better behavior here. 

But it's a difficult field IMO. Let's try the divison by zero. It's easy
and cheap to check before but does many check before really appliying a
division?

And if it's a  expensive operation to check if the input it valid than
raising an exception might be a better idea. So I don't know what should
be the right behavior here.

Regards
Friedrich