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


 package My::Stringlike::Object;

 use overload::substr;

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



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.


  • 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.


With thanks to Matt S Trout <> for suggesting the possibility, and Joshua ben Jore <> for the inspiration by way of UNIVERSAL::ref.


Paul Evans <>