Re^4: How exactly does no work?

[sundialsvc4]

Okay, let’s just cut to the chase here.   use is somewhat of an “overloaded” construct in Perl.   It can be employed to reference an outside module (use foo;), or as a pragma to request certain compile-time behavior (use strict;).

When I typed in what you entered as a “one-liner,” I got various compilation errors (as I should have).   There are several things quite wrong with the code ... undeclared variables, parentheses, and so forth.   On my system it will not compile at all.   If I add my ($b, $d); I get no output at all because of course everything is now undef.   So I am just going to set that (non-)example completely aside.

no warnings; like its brother use warnings;, is a compile-time directive.   It instructs Perl to behave in different ways when compiling your source-code into its internal form for execution.   One form countermands the other.   I do not profess to know the whys and wherefores of these things because the one thing that I do know is how to use them correctly, which IMHO is:

• At the top of every Perl program that you write, use strict; use warnings;.
• In the extremely rare case where you are forced to do something that these declarations would prevent, and you cannot find another way (translation:   you haven’t looked hard enough yet, e.g. at UNIVERSAL), then you should bracket the smallest portion of code necessary.   Insert no warnings;, then do the minimal amount of work, then immediately use warnings; again ... having first inserted a prodigious comment explaining exactly why you had to do this.

[chromatic]

use is somewhat of an “overloaded” construct in Perl. It can be employed to reference an outside module (use foo;), or as a pragma to request certain compile-time behavior (use strict;).

I think that explanation confuses more than it enlightens. In both cases (pragma and module), use does the same thing:

BEGIN
{
    require 'Module.pm':
    'Module'->import;
};

It always performs the require (modulo Perl's internal cache of what it's already loaded) and it always performs the import (modulo use Foo ();). use has no idea of whether what it's loading is a pragma. That part's up to the loaded thing's import() method.