A feature of use

[ambrus]

Look at the following snippet.

perl -e 'open strict, ">&", STDOUT or die; use strict; print strict fo
+obar, "\n";'

This prints foobar so clearly foobar is interpretted as a bareword. However, we use strict, so that should disallow barewords. Why is this? (The title of the post can give a hint.)

[ambrus]

In fact, even this works.

perl -e 'if (0) { open strict; } use strict; print STDOUT foobar, "\n"
+;'

[jdalbec]

Is this related to Filehandles vs. Packages: And the winner is...?

[bart]

Ah, you gave me enough clues...
use strict is turned into require strict; which loads the module, followed by strict->import;. But Perl now knows strict as a filehandle, so this syntax is treated as an object method call to the filehandle object associated with the filehandle with the name "strict".

Since either there is a method for the package IO::Handle (or else, import has a special status so perl won't complain if it can't find it), it works but actually doesn't do much. What it definitely doesn't do is call import for the package strict. That's why strict checks are still off.

So it's all caused by the ambiguous syntax of word->method, which may represent either a class method call, or an object method call.

[tye]

See Universally unimportant and overused. UNIVERSAL imports import(). Bleh.

[ambrus]

It certainly seems so, we can even verify this like this.

perl -we 'use IO::Handle; { package IO::Handle; sub import { warn "imp
+ort called on handle $_[0]"; } } if (0) { open strict; } BEGIN { warn
+ "about to use strict"; } use strict; BEGIN { warn "after use strict"
+; } use warnings;'

However, I don't understand why this happens even before the open is called at all. I originally wrote the snippet with open in a BEGIN, because I thought that was the only way to trigger this. In fact, as open $foo, ... should autovivify a new glob with filehandle each time it's executed, I don't really know why open strict should do anything in compile time.

Indeed, notice how my $h = *strict; open $h; triggers the feature if it's ran in a BEGIN block before use strict;, but not if it's just compiled before it.

[ambrus]

See also Prevent Strings From Being Interpreted As A File Handle (thanks to choroba for the link).