Context propagates.

sub handle_mutator {
    my ($self,$cb)=@_;
    my $obj;
    if (defined wantarray) {
        $obj = $self->copy();
    } else {
        $obj = $self;
    };
    $cb->($obj,@_);
}


sub something {
    shift->handle_mutator(sub{ .... });
}
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