There are a lot of parallels, and similar syntax, but the Real Important Stuff is very different. Memory management, for three or more.

Perl lexicals are like C auto variables, which are generally at the top of the stack.

C++ references are like Perl aliases. They have value semantics, but are pointers under the skin. Perl references are like C/C++ pointers.

Perl lexicals are like C auto variables, which are generally at the top of the stack.

That is somewhat true and somewhat misleading.

Perl lexicals don't go on the stack. They can't because of the key difference between Perl lexicals and C lexicals: The lifetime of C lexicals matches their scope while Perl lexicals can live forever.

That is, a C lexical is destroyed unconditionally when its scope is exitted. Perl lexicals are initialized (often creating a new instance) when their scope is entered and have one reference to them removed when the scope is exitted. The variable instance will only be destroyed if that was the only remaining reference to it.

So having a sub return a pointer/reference to one of its lexical variables in C/C++ is "a bug" (as it storing a pointer/reference into something that will live past the call into the sub). Having a Perl sub (or 'do' block, etc.) return a reference to one of its lexicals is just fine (as is storing references to any variables anywhere -- though making circular references causes other, less severe, problems).

- tye        

Is there any way, in Perl, to create an alias to a lexical?

Data::Alias and/or Lexical::Alias, depending on what version of Perl you're using.

Is there any way, in Perl, to create an alias to a lexical?

my $foo = "foo";
for my $bar ($foo) {$bar = "bar"}
print $foo;
__END__
bar
[download]

Lexicals seem very different to me from anything there's in C, am I wrong?

This also demonstrates that the for variable is an alias, and not a copy:

my $foo = "foo";
for my $bar ($foo) 
{
    print "foo: $foo, ", \$foo, "\n";
    print "bar: $bar, ", \$bar, "\n";
    $bar = "bar";
    print "foo: $foo, ", \$foo, "\n";
    print "bar: $bar, ", \$bar, "\n";
}

print "foo: $foo, ", \$foo, "\n";
__OUTPUT__
foo: foo, SCALAR(0x18245f0)
bar: foo, SCALAR(0x18245f0)
foo: bar, SCALAR(0x18245f0)
bar: bar, SCALAR(0x18245f0)
foo: bar, SCALAR(0x18245f0)
__END__
[download]

-QM
--
Quantum Mechanics: The dreams stuff is made of

Lexicals seem very different to me from anything there's in C, am I wrong?

A lexicals usually behaves like a stack variable. However, that breaks down when closures are used (e.g. do { my $lex; sub { return \$lex; } }), or when the address of the lexical is copied outside of the lexical's scope (e.g. my @a; { my $lex; push(@a, \$lex); } and do { my $lex; \$lex }).

A lexical always behaves like a ref-counted pointer (stack variable) to dynamically allocated memory (heap variable). In other words,
my $scalar;
is something like
ref_ptr<scalar_t> scalar = new scalar_t();

Is there any way, in Perl, to create an alias to a lexical?

Yes:
our $sym; local *sym = \$lexical;

However, I think you meant to ask if there was a way to alias a lexical to something else. I think
for my $lexical ($var)
is the only way provided by the language, but there might be other ways interally. If so, there might be an XS module that does this.