From: see_signature@127.0.0.1
Date: 2001-05-02T09:10:08+09:00
Subject: [ruby-talk:14518] problems with String -> Numeric conversions

Hi Experts,

Ruby has a number of very useful functions which convert strings representing
numbers into actual numbers:

    String#to_i
    String#to_f
    String#hex
    String#oct

For some reason, which I cannot yet comprehend, these conversion functions
provide NO ERROR HANDLING (no exceptions ever raised, no NaN ever returned).  

A string which does not correspond to any number is silently converted to
zero. Therefore, if the outcome of a conversion is number zero, one cannot tell
for sure whether this zero comes from a legitimate string representing number
zero or from some guffy broken corrupted string:

    a = "0".to_i  # -> 0
    b = "garbage".to_i  # -> 0
    a == b  # -> true

The bugs which may result from this behavior can be very severe. A program can
still run to completion but deliver incorrect results because the input
integrity has been violated.

I think that it will be useful if these conversion function perform some  format
validation. Since changes to core Ruby is a delicate and time consuming issue,
here is a Ruby reimplementation of String#to_i and String#to_f which checks for 
correct format and raises an exception on error.
Also, String#to_i distinguishes between decimal, octal and hexadecimal notations
and parse these numbers accordingly.

Any comments and feedback appreciated

--Leo-- [ slonika AT yahoo DOT com ]

####  RUBY  CODE  FOLLOWS  ####

# Conversion from a String to Numbers should raise an exception if the string has
# an improper format. Strangely enough, Ruby's standard conversion functions do not
# provide for any kind of error handling and return number '0' on failure.
# Therefore, in Ruby one cannot possibly distinguish between these two cases:
#       "0".to_i             # -> 0
#       "not-a-number".to_i  # -> 0

# The following code augments standard conversion functions String#to_i and
# String#to_f with the error handling code so that an attempt to convert a
# string not suited for numeric conversion will raise NumericError exception.

class NumericError < RuntimeError
end

class String
  alias __std__to_i to_i   if ! method_defined? :__std__to_i
  alias __std__to_f to_f   if ! method_defined? :__std__to_f
  alias __std__hex  hex    if ! method_defined? :__std__hex
  alias __std__oct  oct    if ! method_defined? :__std__oct
  
  def to_i()
    case self 
    when /^[-+]?0\d/         then  __std__oct
    when /^[-+]?0x[a-f\d]/i  then  __std__hex
    when /^[-+]?\d/          then  __std__to_i
    else raise NumericError, "Cannot convert string to Integer!"
    end
  end

  def to_f()
    case self
    when /^[-+]?\d/  then  __std__to_f
    else raise NumericError, "Cannot convert string to Float!"
    end
  end
end
################################################################################

#EOF