From @cpansprout

The way prototypes are applied to subroutines is not consistent. I’m not sure how these cases should work​:

sub foo {} # has a body already
sub foo ($);
print prototype \&foo;

That gives me a ‘Prototype mismatch’ warning and does not apply the prototype.

sub MODIFY_CODE_ATTRIBUTES{}
sub foo {} # has a body already
sub foo ($) :Frigid;
print prototype \&foo;

That gives me a ‘Prototype mismatch’ warning, but *does* apply the prototype. (In 5.10 it does not apply it.)

So now I’ve discovered a new feature!

Also, this case does apply the prototype, but that’s to be expected, as the sub is not defined​:

sub foo($);
sub foo(;$); # warning, but the prototype is applied anyway
print prototype \&foo;

But in this case, the prototype is not applied​:

sub bar($);
BEGIN { *foo = \&bar }
sub foo(;$); # warns
print prototype \&foo;

And here the prototype is silently ignored​:

BEGIN { *foo = \&bar }
sub foo($);
print prototype \&foo;

Flags​:
  category=core
  severity=low

Site configuration information for perl 5.14.0​:

Configured by sprout at Wed May 11 13​:45​:58 PDT 2011.

Summary of my perl5 (revision 5 version 14 subversion 0) configuration​:
  Snapshot of​: eb70bb4
  Platform​:
  osname=darwin, osvers=10.5.0, archname=darwin-thread-multi-2level
  uname='darwin pint.local 10.5.0 darwin kernel version 10.5.0​: fri nov 5 23​:20​:39 pdt 2010; root​:xnu-1504.9.17~1release_i386 i386 '
  config_args='-Dusedevel -de -Duseithreads -Doptimize=-g'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=define, usemultiplicity=define
  useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
  use64bitint=undef, use64bitall=undef, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-fno-common -DPERL_DARWIN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include',
  optimize='-g',
  cppflags='-fno-common -DPERL_DARWIN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
  ccversion='', gccversion='4.2.1 (Apple Inc. build 5664)', gccosandvers=''
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib
  libs=-ldbm -ldl -lm -lutil -lc
  perllibs=-ldl -lm -lutil -lc
  libc=/usr/lib/libc.dylib, so=dylib, useshrplib=false, libperl=libperl.a
  gnulibc_version=''
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
  cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/usr/local/lib -fstack-protector'

Locally applied patches​:
  RC3

@​INC for perl 5.14.0​:
  /usr/local/lib/perl5/site_perl/5.14.0/darwin-thread-multi-2level
  /usr/local/lib/perl5/site_perl/5.14.0
  /usr/local/lib/perl5/5.14.0/darwin-thread-multi-2level
  /usr/local/lib/perl5/5.14.0
  /usr/local/lib/perl5/site_perl
  .

Environment for perl 5.14.0​:
  DYLD_LIBRARY_PATH (unset)
  HOME=/Users/sprout
  LANG=en_US.UTF-8
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/usr/bin​:/bin​:/usr/sbin​:/sbin​:/usr/local/bin​:/usr/X11/bin​:/usr/local/bin
  PERL_BADLANG (unset)
  SHELL=/bin/bash