'use Foobar.12345' is undocumentedly parsed as 'use Foobar ".12345";'

[jimav]

use Foobar.12345; compiles without error and calls Foobar->import("Foobar",0.12345);

I could not find any documentation of this odd behavior.

Is this old parser support for legacy version checking via the Exporter module (which calls $modname->VERSION($arg) for numeric args)? This only works for version numbers < 1.0 so maybe not.

But clearly Perl is parsing this specially.

If this is intentional then the special parsing should be documented in perlfunc ('use'). If not intentional then a parse error might be appropriate.

Steps to Reproduce

echo 'package XX;use Data::Dumper; sub import{ for(@_){print Dumper($_);} } 1;' >/tmp/XX.pm
perl -I/tmp -E 'use XX.12345;'

Result

$VAR1 = 'XX';
$VAR1 = '0.1234';

Expected result

Naively I would assume Perl would search for "XX.12345.pm" in @INC and fail if not found, or possibly complain that "XX.12345" is not a valid module name.

(Perl v5.41.4)

perl_dashV.txt

[Grinnz]

This does not seem odd to me. The critical piece is understanding how an identifier[1] is parsed in Perl, and that whitespace is insignificant in most parsing except to separate identifiers and other tokens. There are likely several other non-word characters that could follow Foobar and be parsed as a new argument to be passed to the import method. Regardless, the ultimate point is that a period is not valid in an identifier or package name.

1. https://perldoc.perl.org/perldata#Identifier-parsing

[xenu]

The critical piece is understanding how an identifier[1] is parsed in Perl,

And that ".123" is a valid way to spell "0.123".

Also, here's an example that doesn't involve use:

print STDOUT.123 (outputs "0.123")

[mauke]

The odd thing is that use Foo .123 parses as use Foo ".123" (import), not use Foo 0.123 (version requirement). I can see from the source code that a version number in use must start with either a digit or v and a digit. This is even documented (in perldoc -f use):

The VERSION argument cannot be an arbitrary expression. It only counts as a VERSION argument if it is a version number literal, starting with either a digit or v followed by a digit. Anything that doesn't look like a version literal will be parsed as the start of the LIST.

Using a space after the module name or not doesn't make a difference to the tokenizer.

[jimav]

@Grinnz - That makes perfect sense and explains the parsing.

The 'use' docs say version numbers must start with a digit, to .123 does not qualify (0.123 does).