[perl #2741] [BUG] version checking doesn't work per apparent docs

[Michael G Schwern via RT]

 [EMAIL PROTECTED] - Tue Mar 28 03:38:58 2000]:
 
 From perldata:
 
A literal of the form `v1.20.300.4000' is parsed as a string
composed of characters with the specified ordinals.    Such
literals are accepted by both `require' and `use' for doing a
version check.
 
 This is not true, however.  Witness:
 
 % perl -MIO::File -le 'print IO::File::-VERSION
 1.08
 
 % perl -e 'use IO::File  1.08'
 
 % perl -e 'use IO::File  v1.08'
 Octal number in vector unsupported at -e line 1, at end of line
 BEGIN not safe after errors--compilation aborted at -e line 1.
 
 # vector?  qu'est-ce que c'est qu'un vector? 
 # did I vec() something for select()?
 
 % perl -e 'use IO::File  1.8'
 IO::File version 1.8 required--this is only version 1.08 at -e line 1.
 BEGIN failed--compilation aborted at -e line 1.
 
 % perl -e 'use IO::File  v1.8'
 
 % perl -e 'use IO::File  1.8.2'
 
 % perl -e 'use IO::File  v1.8.2'
 
 % perl -e 'use IO::File  1.9.2.20'
 
 % perl -e 'use IO::File  v1.9.2.20'
 
 % perl -e 'use IO::File  1.9.9'
 
 % perl -e 'use IO::File  1.9..999'
 
 % perl -e 'use IO::File  v1.9.9'
 
 % perl -e 'use IO::File  v1.9..999'
 
 ### Ick ick ick!  Something sure smells pretty icthy around here.
 
 # And here's some naive stuff.  Remember: version were always numbers
 # before.  So one expects numbers to continue to work.  But they don't.
 # And produce very odd msgs.
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION   1.8'
 0
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION   v1.8'
 1
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION   1.8'
 1
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION   v1.8'
 0
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION == 1.08'
 1
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION == v1.08'
 Octal number in vector unsupported at -e line 1, at end of line
 Execution of -e aborted due to compilation errors.
 
 # octal huh?
 
 % perl -MIO::File -e 'printf %d\n, IO::File::-VERSION == v1.80'
 Octal number in vector unsupported at -e line 1, at end of line
 Execution of -e aborted due to compilation errors.
 
 % perl -MIO::File -we 'printf %d\n, IO::File::-VERSION == v1.80'
 Argument ^AP isn't numeric in numeric eq (==) at -e line 1.
 0
 
 # That's disgusting.  Run it through uncontrol!

v1.2.3 style version strings are being phased out and should be
replaced by the various options presented by version.pm.

All the above now works in 5.8.6 with the exception of the final
Argument ^AP isn't numeric warning which is still there.  As version
strings are going bye-bye will that ever be fixed?

Re: [perl #2741] [BUG] version checking doesn't work per apparent docs

[John Peacock]

Michael G Schwern via RT wrote:

v1.2.3 style version strings are being phased out and should be
replaced by the various options presented by version.pm.


Well, no, not exactly.  v1.2.3 versions are likely to be the preferred format 
for Perl6 (AIUI), but the leading 'v' won't be a v-string any longer but rather 
a fullblown version number.  It's true that the version.pm module will permit 
compatibility for older Perl's, but the following are completely equivalent 
(under v5.9.3+):


package oldstyle;
use version;
our $VERSION = version-new(v1.2.3);

package newtyle;
our $VERSION = v1.2.3;

OK, I'm fibbing a little in that the first package will have a version object 
and the second will not (although I have a patch to do so), but both of them 
will emerge from UNIVERSAL::VERSION completely identically, i.e. as 1.002003). 
See below for why that distinction is important.




All the above now works in 5.8.6 with the exception of the final
Argument ^AP isn't numeric warning which is still there.  As version
strings are going bye-bye will that ever be fixed?


It shouldn't be fixed, because the naive tests Tom was making in the second half 
of the bug were based on a flawed understanding of how the UNIVERSAL::VERSION 
sub operated then or now.  When called as a class method like 
IO::File::-VERSION, UNIVERSAL::VERSION merely returns the contents of the 
package $VERSION scalar.  As such, any special handling due to v-string, etc, 
doesn't happen at all.  And so there is no way that a bare == comparison will 
know anything about how to handle version comparisons vs. v-strings.


The only way to see whether the v-string versions are handled properly in Perl 
5.8.1+ is to 'use package v1' (and hence why all of the first half of the bug 
report now work fine).  It is not currently possible to compare a version number 
to a bare v-string and unless I make $VERSION a magical scalar to automatically 
upgrade to version objects (a patch I currently have working, BTW), it won't 
ever be possible in the general case.


With the patch I have to automatically upgrade the package $VERSION scalar to a 
version object, the following becomes true:



$ LD_LIBRARY_PATH=$PWD ./perl -Ilib -MIO::File -we 'print ref 
$IO::File::VERSION'
version



$ LD_LIBRARY_PATH=$PWD ./perl -Ilib -MIO::File -we 'printf %d\n, 
$IO::File::VERSION == v1.120'
1



$ LD_LIBRARY_PATH=$PWD ./perl -Ilib -MIO::File -we 'printf %d\n, 
$IO::File::VERSION == v1.121'
0


but when called as a package method, UNIVERSAL::VERSION returns the *numified* 
representation of the underlying version object, not the version object itself, 
so this will still warn:



$ LD_LIBRARY_PATH=$PWD ./perl -Ilib -MIO::File -we 'printf %d\n, 
IO::File::-VERSION == v1.120'
Argument ^Ax isn't numeric in numeric eq (==) at -e line 1.
0


I have delayed closing this ticket mostly through inertia.  With this 
explanation appended, it can now be safely closed I think.


John

--
John Peacock
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