Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Missing warning 'scalar value better written as...' when using reference #16277

Open
p5pRT opened this issue Nov 24, 2017 · 7 comments
Open

Missing warning 'scalar value better written as...' when using reference #16277

p5pRT opened this issue Nov 24, 2017 · 7 comments

Comments

@p5pRT
Copy link

@p5pRT p5pRT commented Nov 24, 2017

Migrated from rt.perl.org#132502 (status was 'open')

Searchable as RT132502$

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 24, 2017

From @epa

Created by @epa

% perl -wE '@​x = (1, 2, 3); say @​x[1]'
Scalar value @​x[1] better written as $x[1] at -e line 1.
2
% perl -wE '$x = [ 1, 2, 3 ]; say @​$x[1]'
2

The second use should also make a warning, along the lines of

  Scalar value @​$x[1] better written as $x->[1]

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl 5.22.2:

Configured by Red Hat, Inc. at Fri Nov  4 14:35:02 UTC 2016.

Summary of my perl5 (revision 5 version 22 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=4.7.9-200.fc24.x86_64, archname=x86_64-linux-thread-multi
    uname='linux buildvm-12.phx2.fedoraproject.org 4.7.9-200.fc24.x86_64 #1 smp thu oct 20 14:26:16 utc 2016 x86_64 x86_64 x86_64 gnulinux '
    config_args='-des -Doptimize=none -Dccflags=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic -Dldflags=-Wl,-z,relro  -Dccdlflags=-Wl,--enable-new-dtags -Wl,-z,relro  -Dlddlflags=-shared -Wl,-z,relro  -Dshrpdir=/usr/lib64 -DDEBUGGING=-g -Dversion=5.22.2 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dprefix=/usr -Dvendorprefix=/usr -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl5 -Dsitearch=/usr/local/lib64/perl5 -Dprivlib=/usr/share/perl5 -Dvendorlib=/usr/share/perl5/vendor_perl -Darchlib=/usr/lib64/perl5 -Dvendorarch=/usr/lib64/perl5/vendor_perl -Darchname=x86_64-linux-thread-multi -Dlibpth=/usr/local/lib64 /lib64 /usr/lib64 -Duseshrplib -Dusethreads -Duseithreads -Dusedtrace=/usr/bin/dtrace -Duselargefiles -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dscriptdir=/usr/bin -Dusesitecustomize'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='  -g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include'
    ccversion='', gccversion='5.3.1 20160406 (Red Hat 5.3.1-6)', 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='gcc', ldflags ='-Wl,-z,relro  -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib64 /lib64 /usr/lib64 /usr/local/lib /usr/lib /lib/../lib64 /usr/lib/../lib64 /lib
    libs=-lpthread -lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -lresolv -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.22.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.22'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,--enable-new-dtags -Wl,-z,relro '
    cccdlflags='-fPIC', lddlflags='-shared -Wl,-z,relro  -L/usr/local/lib -fstack-protector-strong'

Locally applied patches:
    Fedora Patch1: Removes date check, Fedora/RHEL specific
    Fedora Patch3: support for libdir64
    Fedora Patch4: use libresolv instead of libbind
    Fedora Patch5: USE_MM_LD_RUN_PATH
    Fedora Patch6: Skip hostname tests, due to builders not being network capable
    Fedora Patch7: Dont run one io test due to random builder failures
    Fedora Patch15: Define SONAME for libperl.so
    Fedora Patch16: Install libperl.so to -Dshrpdir value
    Fedora Patch22: Document Math::BigInt::CalcEmu requires Math::BigInt (CPAN RT#85015)
    Fedora Patch26: Make *DBM_File desctructors thread-safe (RT#61912)
    Fedora Patch27: Make PadlistNAMES() lvalue again (CPAN RT#101063)
    Fedora Patch28: Make magic vtable writable as a work-around for Coro (CPAN RT#101063)
    Fedora Patch29: Fix duplicating PerlIO::encoding when spawning threads (RT#31923)
    Fedora Patch30: Do not let XSLoader load relative paths (CVE-2016-6185)
    Fedora Patch31: Avoid loading optional modules from default . (CVE-2016-1238)
    Fedora Patch32: Fix a crash in lexical scope warnings (RT#128597)
    Fedora Patch33: Do not mangle errno from failed socket calls (RT#128316)
    Fedora Patch34: Fix crash in "evalbytes S" (RT#129196)
    Fedora Patch35: Fix crash in "evalbytes S" (RT#129196)
    Fedora Patch36: Fix crash in "evalbytes S" (RT#129196)
    Fedora Patch37: Fix crash in splice (RT#129164, RT#129166, RT#129167)
    Fedora Patch38: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch39: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch40: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch41: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch42: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch43: Fix crash when matching UTF-8 string with non-UTF-8 substrings (RT#129350)
    Fedora Patch44: Fix parsing perl options in shell bang line (RT#129336)
    Fedora Patch45: Fix firstchar bitmap under UTF-8 with prefix optimization (RT#129950)
    Fedora Patch46: Avoid infinite loop in h2xs tool if enum and type have the same name (RT130001)
    Fedora Patch47: Fix stack handling when calling chdir without an argument (RT#129130)
    Fedora Patch200: Link XS modules to libperl.so with EU::CBuilder on Linux
    Fedora Patch201: Link XS modules to libperl.so with EU::MM on Linux


@INC for perl 5.22.2:
    /home/eda/lib64/perl5/
    /usr/local/lib64/perl5
    /usr/local/share/perl5
    /usr/lib64/perl5/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib64/perl5
    /usr/share/perl5


Environment for perl 5.22.2:
    HOME=/home/eda
    LANG=en_GB.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=C
    LC_CTYPE=en_GB.UTF-8
    LC_MESSAGES=en_GB.UTF-8
    LC_MONETARY=en_GB.UTF-8
    LC_NUMERIC=en_GB.UTF-8
    LC_TIME=en_GB.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/eda/bin:/home/eda/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/sbin:/home/eda/.local/bin:/home/eda/bin:/sbin:/usr/sbin
    PERL5LIB=/home/eda/lib64/perl5/
    PERL_BADLANG (unset)
    SHELL=/bin/bash

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 27, 2017

From @xsawyerx

On 11/24/2017 12​:27 PM, Ed Avis (via RT) wrote​:

# New Ticket Created by "Ed Avis"
# Please include the string​: [perl #132502]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=132502 >

This is a bug report for perl from eda@​waniasset.com,
generated with the help of perlbug 1.40 running under perl 5.22.2.

-----------------------------------------------------------------
[Please describe your issue here]

% perl -wE '@​x = (1, 2, 3); say @​x[1]'
Scalar value @​x[1] better written as $x[1] at -e line 1.
2
% perl -wE '$x = [ 1, 2, 3 ]; say @​$x[1]'
2

The second use should also make a warning, along the lines of

Scalar value @​$x[1] better written as $x->[1]

I think that's a preference in style. While I personally dislike the
style, it is not a mistake to do so.

The warning for "scalar value better written as" refers to the context
and has an effect on assignment, which is a behavioral difference.

@​foo[ bar() ] = baz(); # List context
$foo[ bar() ] = baz(); # scalar context

So it's better to warn here because it's likely not what you wanted if
you're explicitly accessing a single index.

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 27, 2017

The RT System itself - Status changed from 'new' to 'open'

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 27, 2017

From @Smylers

Sawyer X <xsawyerx@​gmail.com> writes​:

On 11/24/2017 12​:27 PM, Ed Avis (via RT) wrote​:

% perl -wE '@​x = (1, 2, 3); say @​x[1]'
Scalar value @​x[1] better written as $x[1] at -e line 1.
2
% perl -wE '$x = [ 1, 2, 3 ]; say @​$x[1]'
2

The second use should also make a warning, along the lines of

Scalar value @​$x[1] better written as $x->[1]

I think that's a preference in style. While I personally dislike the
style, it is not a mistake to do so.

The warning for "scalar value better written as" refers to the context
and has an effect on assignment, which is a behavioral difference.

@​foo[ bar() ] = baz(); # List context
$foo[ bar() ] = baz(); # scalar context

That context difference still applies with references​:

  @​$foo[0] = qw<first middle last>; # 'first'
  $foo->[0] = qw<first middle last>; # 'last'

The matter of style is that the scalar context one can also be written​:

  $$foo[0] = qw<first middle last>; # 'last'
 
Smylers

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 27, 2017

From @epa

Sawyer X, thanks for your reply. If I understand you correctly, you say that the warning is intended for the use of @​x[1] as an lvalue. What I do not understand is why it makes sense to treat @​$x[1] differently.

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 27, 2017

From Eirik-Berg.Hanssen@allverden.no

On Mon, Nov 27, 2017 at 10​:50 AM, Smylers <smylers@​stripey.com> wrote​:

Sawyer X <xsawyerx@​gmail.com> writes​:

On 11/24/2017 12​:27 PM, Ed Avis (via RT) wrote​:

% perl -wE '@​x = (1, 2, 3); say @​x[1]'
Scalar value @​x[1] better written as $x[1] at -e line 1.
2
% perl -wE '$x = [ 1, 2, 3 ]; say @​$x[1]'
2

The second use should also make a warning, along the lines of

Scalar value @​$x[1] better written as $x->[1]

I think that's a preference in style. While I personally dislike the
style, it is not a mistake to do so.

The warning for "scalar value better written as" refers to the context
and has an effect on assignment, which is a behavioral difference.

@​foo[ bar() ] = baz(); # List context
$foo[ bar() ] = baz(); # scalar context

That context difference still applies with references​:

@​$foo[0] = qw<first middle last>; # 'first'
$foo->[0] = qw<first middle last>; # 'last'

The matter of style is that the scalar context one can also be written​:

$$foo[0] = qw<first middle last>; # 'last'

  So, a less confusing warning would be​: "Scalar value @​$x[1] better
written as $$x[1]". (A minimal difference is more to the point, right?)

  Or for a more thorough approach​: "Scalar value @​$x[1] better written as
$$x[1] (or equivalently, $x->[1])".

Eirik

<http​://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
Virus-free.
www.avg.com
<http​://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

@p5pRT
Copy link
Author

@p5pRT p5pRT commented Nov 27, 2017

From @xsawyerx

On 11/27/2017 02​:31 PM, Eirik Berg Hanssen wrote​:

On Mon, Nov 27, 2017 at 10​:50 AM, Smylers <smylers@​stripey.com
<mailto​:smylers@​stripey.com>> wrote​:

Sawyer X \<xsawyerx@&#8203;gmail\.com \<mailto&#8203;:xsawyerx@&#8203;gmail\.com>> writes&#8203;:

> On 11/24/2017 12&#8203;:27 PM\, Ed Avis \(via RT\) wrote&#8203;:
>
> > % perl \-wE '@&#8203;x = \(1\, 2\, 3\); say @&#8203;x\[1\]'
> > Scalar value @&#8203;x\[1\] better written as $x\[1\] at \-e line 1\.
> > 2
> > % perl \-wE '$x = \[ 1\, 2\, 3 \]; say @&#8203;$x\[1\]'
> > 2
> >
> > The second use should also make a warning\, along the lines of
> >
> >   Scalar value @&#8203;$x\[1\] better written as $x\->\[1\]
>
> I think that's a preference in style\. While I personally dislike the
> style\, it is not a mistake to do so\.
>
> The warning for "scalar value better written as" refers to the
context
> and has an effect on assignment\, which is a behavioral difference\.
>
> @&#8203;foo\[ bar\(\) \] = baz\(\); \# List context
> $foo\[ bar\(\) \] = baz\(\); \# scalar context

That context difference still applies with references&#8203;:

  @&#8203;$foo\[0\]  = qw\<first middle last>;  \# 'first'
  $foo\->\[0\] = qw\<first middle last>;  \# 'last'

The matter of style is that the scalar context one can also be
written&#8203;:

  $$foo\[0\]  = qw\<first middle last>;   \# 'last'

  So, a less confusing warning would be​: "Scalar value @​$x[1] better
written as $$x[1]".  (A minimal difference is more to the point, right?)

  Or for a more thorough approach​: "Scalar value @​$x[1] better written
as $$x[1] (or equivalently, $x->[1])".

Make it ${$x}[1] and you have got yourself a deal. :)

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Projects
None yet
Linked pull requests

Successfully merging a pull request may close this issue.

None yet
1 participant