A dispatch table

my %dispatch_table = (
    foo => \&foo,
    bar => sub { mumble; },
);
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A sub returning a sub generated on the fly, maybe a closure,

sub generate {
    my $foo = shift;
    sub { $foo };
}
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A variable routine to be called,

sub callit {
    my $sub = shift;
    $sub->(@_);
}
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Overriding a sub,

# in a scope . . .
    local *foo = generate 'bar';
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The list goes on . . .