This and other RFCs are available on the web at http://dev.perl.org/rfc/ =head1 TITLE Perl should not abort when a required file yields a false value =head1 VERSION Maintainer: Dominus <[EMAIL PROTECTED]> Date: 21 Sep 2000 Last Modified: 23 Sep 2000 Mailing List: [EMAIL PROTECTED] Number: 269 Version: 2 Status: Withdrawn See Also: RFC 55 =head1 STATUS This proposal is withdrawn because it duplicates RFC 55, "Compilation: Remove requirement for final true value in require-d and do-ed files" =head1 ABSTRACT Modules should not have to end with C<1;>. It is silly and confusing. =head1 DESCRIPTION Modules typically contain subroutine definitions. A module may contain initialization code also. If the initialization code fails, the module can return a false value to its caller, which aborts the compilation. In Perl 5, a module that contains nothing but subroutine definitions will return false by default, necessitating a 1; at the bottom. If the C<1;> is omitted, Perl emits the error Foo.pm did not return a true value... In spite of plenty of documentation, people Frequently Ask what this error means. Some languages like to have the compiler emit annoying messages to announce you forgot to include some pointless code whose only purpose is to stop the compiler from emitting the annoying message. Perl is mostly free of such nonfeatures. I propose that this unfeature be dropped entirely. No useful functionality is lost. If a Perl 6 module wants to indicate an initialization failure by throwing a fatal exception, it can simply call C<die>. If the calling module wants to abort when a C<require>d file returns a false value, it is free to do that. The 'module initialization' feature is little-used. 99 the of 102 files in Perl 5.6 lib/*.{pl,pm} end with C<1;>. AnyDBM_File invokes 'die' explicitly. The only real exceptions are diagnostics.pm and timelocal.pl. =head1 IMPLEMENTATION 'require' should execute code in a file and return the result, as before, but it should not call Perl_die when the result is false. However, see below. =head1 MIGRATION In 98% of cases, no translation is necessary. The first version of the translator can ignore the issue entirely. Strategies to cover the other 2% follow: Is general, direct source translation of this feature of Perl 5 modules would probably be impossible. It's tempting to say that the translator should simply translate the last statement or block in the module from this: STATEMENT to this: unless (do {STATEMENT}) { require Carp; Carp::croak "... did not return a true value"; } However, I think that is impractical. The module might contain code that looks like this: if (something()) { return $v1; } ... $v2; In this case the 'return $v1' statement would I<also> have to be translated. In general, there might be many, many statements that would need to be translated. This would look awful. I think that if complete coverage is desired, the best choice would be to introduce a new pragma, which would enable the old behavior. A translated module would begin with package Foo; use perl5 'require/use semantics'; ... When this file was C<require>d, the pragma would set a flag. The C<pp_require> opcode would check the flag after compiling the file, and would call C<Perl_die> as before if the file returned a false value and if the flag was set. If Foo C<require>d any other modules, the flag would be cleared before loading them, and restored again afterwards. (That is, the flag would have file scope.) =head1 REFERENCES Perl on-line manuals
