class feature: Anonymous methods can't access fields

[ivrntsv]

Description
I'm not sure if they should, but, maybe, someone knows better.

Steps to Reproduce
perl -Mexperimental=class -e 'class Foo; field $foo = 42; use overload q{""} => method (@) { $foo }'
gives
Field $foo is not accessible outside a method at -e line 1.

Perl configuration

Summary of my perl5 (revision 5 version 42 subversion 0) configuration:
   
  Platform:
    osname=cygwin
    osvers=3.6.3-bc3e285a.x86_64
    archname=x86_64-cygwin
    uname='cygwin_nt-10.0-19045 desktop-97pareg 3.6.3-bc3e285a.x86_64 2025-06-23 18:27 utc x86_64 cygwin '
    config_args='-des -Uusethreads -Dfirstmakefile=GNUmakefile -Doptimize=-march=nocona -msahf -mtune=generic -O2 -pipe -Dprefix=/usr -Dprivlib=/usr/share/perl/core -Darchlib=/usr/lib/perl/core -Dsitelib=/usr/share/perl/site -Dsitearch=/usr/lib/perl/site -Dinc_version_list=none -Dman1dir=none -Dman3dir=none -Darchname=x86_64-cygwin -Dlibperl=msys-perl5_42.dll -Dcc=gcc -Dld=g++ -Accflags=-march=nocona -msahf -mtune=generic -O2 -pipe -DNO_TAINT_SUPPORT -fwrapv'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='gcc'
    ccflags ='-D_GNU_SOURCE -march=nocona -msahf -mtune=generic -O2 -pipe -DNO_TAINT_SUPPORT -fwrapv -fno-strict-aliasing -fstack-protector-strong -D_FORTIFY_SOURCE=2'
    optimize='-march=nocona -msahf -mtune=generic -O2 -pipe'
    cppflags='-D_GNU_SOURCE -march=nocona -msahf -mtune=generic -O2 -pipe -DNO_TAINT_SUPPORT -fwrapv -fno-strict-aliasing -fstack-protector-strong'
    ccversion=''
    gccversion='13.4.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='g++'
    ldflags =' -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,--enable-auto-image-base -fstack-protector-strong'
    libpth=/usr/lib /usr/lib/w32api
    libs=-lpthread -lgdbm -ldb -ldl -lcrypt -lgdbm_compat
    perllibs=-lpthread -ldl -lcrypt
    libc=/usr/lib/libcygwin.a
    so=dll
    useshrplib=true
    libperl=msys-perl5_42.dll
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=dll
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags=' --shared  -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,--enable-auto-image-base -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_STRTOLD
    HAS_TIMES
    NO_TAINT_SUPPORT
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under cygwin
  Compiled at Jul  3 2025 16:25:50
  %ENV:
    PERLLIB="/home/iv/.my/perl"
  @INC:
    /home/iv/.my/perl
    /usr/lib/perl/site
    /usr/share/perl/site
    /usr/lib/perl/core
    /usr/share/perl/core

[mauke]

Anonymous methods themselves are fine:

$ perl -Mexperimental=class -wE 'my $meth; class Foo { field $foo = 42; $meth = method (@) { $foo } }; my $o = Foo->new; say $o->$meth'
42

What doesn't seem to work is method at BEGIN (i.e. compile) time:

$ perl -Mexperimental=class -e 'class Foo; field $foo = 42; use constant HUH => method (@) { $foo }'
Field $foo is not accessible outside a method at -e line 1.

This affects named methods, too:

$ perl -Mexperimental=class -e 'class Foo; field $foo = 42; BEGIN { method asdf(@) { $foo } }'
Field $foo is not accessible outside a method at -e line 1.

[richardleach]

Are the failing examples instances of trying to use $foo before an actual object instance of it has been created?

[ivrntsv]

@richardleach, yes.

[mauke]

@richardleach No.

[ivrntsv]

I'll explain my reply. After some thinking I understood that in my example there is no object creation, hence no fields. @mauke pointed out that it's compile vs run time at play. And there are no fields at compile time. So, solution is to postpone getting field value till runtime after object creation, like:
perl -Mexperimental=class -e 'class Foo; field $foo :reader = 42; use overload q{""} => method (@) { $self->foo }'
I guess it's a limitation of the implementation based on lexical scope. Though, my guess could be wrong.