NAME
    "overload::substr" - overload Perl's "substr()" function

SYNOPSIS
     package My::Stringlike::Object;

     use overload::substr;

     sub _substr
     {
        my $self = shift;
        if( @_ > 2 ) {
           $self->replace_substr( @_ );
        }
        else {
           return $self->get_substr( @_ );
        }
     }

     ...

DESCRIPTION
    This module allows an object class to overload the "substr" core
    function, which Perl's "overload" pragma does not allow by itself.

    It is invoked similarly to the "overload" pragma, being passed a single
    named argument which should be a code reference or method name to
    implement the "substr" function.

     use overload::substr substr => \&SUBSTR;

     use overload::substr substr => "SUBSTR";

    The referred method will be invoked as per core's "substr"; namely, it
    will take the string to be operated on (which will be an object in this
    case), an offset, optionally a length, and optionally a replacement.

     $str->SUBSTR( $offset );
     $str->SUBSTR( $offset, $length );
     $str->SUBSTR( $offset, $length, $replacement );

    In each case, whatever it returns will be the return value of the
    "substr" function that invoked it.

    If the "substr" argument is not provided, it defaults to a method called
    "_substr".

    It is not required that the return value be a plain string; any Perl
    value may be returned unmodified from the "substr" method, or passed in
    as the value of the replacement. This allows objects to behave in
    whatever way is deemed most appropriate.

TODO
    *       More testing - edge cases, especially in LVALUE logic.

    *       Test for memory leaks, especially in LVALUE logic.

    *       Look into / implement fixup of substr() ops compiled before
            module is loaded

    *       Consider if implementations of split(), and "m//" and "s///"
            regexps should be done that also uses the overloaded substr()
            method.

ACKNOWLEDGEMENTS
    With thanks to Matt S Trout <mst@shadowcat.co.uk> for suggesting the
    possibility, and Joshua ben Jore <jjore@cpan.org> for the inspiration by
    way of UNIVERSAL::ref.

AUTHOR
    Paul Evans <leonerd@leonerd.org.uk>

