On 2014-11-01 01:22, Henrik Lindberg wrote:
Somehow fitting, Halloween and all... for what I want to bring up.
Indeed. Cross type interactions are the worst.
Yet again someone was bit by the automatic String to Numeric conversion
that is in Puppet (and also in --parser future).
The particular thing this time was
https://tickets.puppetlabs.com/browse/PUP-3602 that caused certain md5
fingerprints to look like floating point values of value 0 (they all
started with "0e" but had different digits after the e, and since 0 * 10
^something is always 0 the two different md5 fingerprints were reported
to being equal.
Wow.
The best cure is naturally to never do String to numeric conversion. And
we wonder what people feel about that. Should we go for this in Puppet
4.0.0 (and have a 3.7.4 release as the last of the 3x series where this
behavior is implemented when using --parser future).
thirce yes!
The requirement to compare strings and numerals can also be implemented
by converting the numeral to a string (using a canoical non-locale
dependent format). This produces a much safer route, as creating a
string has less degrees of freedom.
There has also been a number of other suggestions how to fix this, that
are less appealing, and for the sake of not having to waste anyone's
time, here they are, with the reasons why they are not so appealing.
* Only convert if LHS is a Number. This makes the order of the
comparison matter and then ($x == $y) != ($y == $x) which is really bad.
* Add === operator to compare both type and value. This is a slippery
slope since we probably want Integer and Float to compare equal - say
0.0 and 0. It adds yet another operator, and we have to decide what
case, selector and in should use since there is no way to specify if one
or the other should be used.
I'd not call that a slope, that's a cliff. See how PHP and javascript
struggle with this.
Instead, since we already have sprintf for value to string conversion,
and there is a scanf in Ruby which does the conversion the other way, we
can simply add that function to core puppet for value conversion.
We could also add to_number(s), or to_number(s, format_string).
When doing that though, we risk ending up with a plethora of to_xxx
functions, and we could instead offer one more universal
convert_to(Type, value, options) function e.g.
Regardless of how you implement it, a good conversion function must be
*strict*. things like "3 Apples" (or md5 hashes) cannot safely be
converted into a number, even if some functions valiantly try.
# best effort, or fail
convert_to(Number, value)
# only if it is an integer, or fail
convert_to(Integer, value, {base => 10})
# convert integer to hex string with some extra text (the sprintf way)
convert_to(String, value, {format => "Hex %x"})
# convert to array of string (give full control over all
# nested conversions.
#
convert_to(Array[String], value, {
Integer => { format => "0x%x" },
Float => { format => "%#.4G" }})
# etc.
So - "Boldly break all the (s)t(r)hings"?
- henrik
--
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