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Re^3: RFC: "assignary" operator ?= :

by shmem (Chancellor)
on Dec 08, 2019 at 17:37 UTC ( #11109843=note: print w/replies, xml ) Need Help??


in reply to Re^2: RFC: "assignary" operator ?= :
in thread RFC: "assignary" operator ?= :

What's the use case which justifies extending Perl's codebase for such an exotic feature?

Concise expressiveness. The ternary ? : is a shortcut for a more convoluted simple if/else

my $var; if($cond) { $var = 'this'; } else { $var = 'that'; }

to be written as

my $var = $cond ? 'this' : 'that';

which is one line compared to 5, 6 or 7, depending on indentation style.

We have more of such subtle operators, eg. ||= vs. //=, where the first checks the LHS truthiness, and the second checks the LHS definedness.

Writing

$var = $var ? 'this' : 'that';

just looks and feels as silly as

$value = $value * 5; $next = $next + 1;

instead of

$value *= 5; $next++;

For the same reasons, I like the compound operator x!! so much, because it lets me set up a parameter list based on truthiness of variables:

$result = build_shed( logs => 24, (screws => 120) x!! @screwdrivers, (nails => 360) x!! @hammers, );

Otherwise, I'd had to say:

my %materials = (logs => 24); $materials{screws} = 120 if @screwdrivers; $materiasl{nails} = 360 if @hammers; $result = build_shed(%materials);

While the second variant is one line less, I regard the first variant as much more readable, and I don't have to introduce a temporary hash just for the sake of building function arguments. Note that in the second variant, the hash name is misspelt as materiasl at the 'nails' case, small bug caught by strict, but annoying. So, instead of

$var = $var ? 'this' : 'that';

I'd rather like to see

$var ?= 'this' : 'that';

because it binds the condition to the LHS in the same way as ||= and //= do.

I can hardly imagine a reason to map non-Boolean values to a previously Boolean $var without confusing any maintainer.

Who said that $var was boolean? It could hold any value, and this value is checked for truthiness.

Anyways - de gustibus non est disputandem.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

Replies are listed 'Best First'.
Re^4: RFC: "assignary" operator ?= :
by choroba (Archbishop) on Dec 08, 2019 at 20:49 UTC
    > I like the compound operator x!!

    It's a bit different than the if/else or ternary it's used to replace, though. Unlike them, the x!! evaluates the left hand side even if the condition is zero. Cf.

    my $t; sub tuple { $t++ => 12 } my $bool = 0; my %h = (tuple()) x !! $bool;
    versus
    ... my %h = $bool ? (tuple()) : ();

    Now %h is the same, but $t is different.

    map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
      It's a bit different than the if/else or ternary it's used to replace, though

      Ah no, this construct doesn't replace any ternary, it is a wholly different thing - but an example for replacement of a convoluted construct with a succinct idiom. Once you grok what x!! is about, you'll never forget what it does.

      perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'
Re^4: RFC: "assignary" operator ?= :
by LanX (Archbishop) on Dec 08, 2019 at 18:42 UTC
    The semantics are already perfectly understood, but you haven't shown us a use case.

    Edit: When and why does this ever happen???

    > $var = $var ? 'this' : 'that';

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

      When and why does this ever happen???

      As for why, I don't know. But it does. On this old debian box:

      qwurx [shmem] ~> libdirs=`perl -E 'say for @INC'` qwurx [shmem] ~> perl -lne 'print "$ARGV: $_" if /\$(\w+)\s+=\s+\$\1\s +*\?/' `(for d in $libdirs; do find $d -type f; done)` /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.pm: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.pm: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.pm: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.pm: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.yp: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.yp: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.yp: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/Treeregexp.yp: $semantic = +$semantic? $semantic->{attr} : undef; /usr/local/share/perl/5.20.2/Parse/Eyapp/eyapp: $opt_s = $opt_s ? 1 : +0; /usr/local/share/perl/5.20.2/Parse/Eyapp/eyapp: $opt_n = $opt_n ? 0 : +1; /usr/local/share/perl/5.20.2/Net/EmptyPort.pm: $proto = $proto ? l +c($proto) : 'tcp'; /usr/local/share/perl/5.20.2/Net/EmptyPort.pm: $proto = $proto ? l +c($proto) : 'tcp'; /usr/local/share/perl/5.20.2/Net/EmptyPort.pm: $proto = $proto ? l +c($proto) : 'tcp'; Can't open /usr/local/share/perl/5.20.2/.Inline.pm.swp: Permission den +ied at -e line 1, <> line 524147. /usr/local/share/perl/5.20.2/ExtUtils/ParseXS.pm: $externC = $exte +rnC ? qq[extern "C"] : ""; /usr/local/share/perl/5.20.2/Test/Builder/Tester.pm: $got = $g +ot ? "$got\n$g" : $g; /usr/local/share/perl/5.20.2/Test/Builder/Tester.pm: $wanted = + $wanted ? "$wanted\n$w" : $w; /usr/local/share/perl/5.20.2/Test/Builder.pm: $test = $test ? 1 : +0; /usr/local/share/perl/5.20.2/Test/Tester/Capture.pm: $test = $test + ? 1 : 0; /usr/local/share/perl/5.20.2/Test2/Compare/Bool.pm: $match = $matc +h ? 0 : 1 if $self->{+NEGATE}; /usr/lib/x86_64-linux-gnu/perl5/5.20/Template/Provider.pm: $parser + = $parser ? $parser->_dump() : '<no parser>'; /usr/lib/x86_64-linux-gnu/perl5/5.20/Template/Provider.pm: + $prev = $prev ? "#$lut->{ $prev }<-": '<undef>'; /usr/lib/x86_64-linux-gnu/perl5/5.20/Template/Provider.pm: + $next = $next ? "->#$lut->{ $next }": '<undef>'; /usr/lib/x86_64-linux-gnu/perl5/5.20/Template/Directive.pm: $line += $line ? " (starting line $line)" : ''; /usr/lib/x86_64-linux-gnu/perl5/5.20/Template/Directive.pm: $args += $args ? "$args, $alias" : ", undef, $alias" /usr/lib/x86_64-linux-gnu/perl5/5.20/DBI/SQL/Nano.pm: if ($neg) { +$match = $match ? 0 : 1; } /usr/share/perl5/SQL/Translator/Producer/Oracle.pm: $i +ndex_name = $index_name ? mk_name( $index_name ) /usr/share/perl5/SQL/Translator/Producer/Oracle.pm: $i +ndex_name = $index_name ? mk_name( $index_name ) /usr/share/perl5/SQL/Translator/Producer/Oracle.pm: $i +ndex_name = $index_name ? mk_name( $index_name ) /usr/share/perl5/SQL/Translator/Producer/Oracle.pm: $d +efault = $default ? "'1'" : "'0'"; /usr/share/perl5/SQL/Abstract.pm: $sql = $sql ? $self->_sqlcase(' wh +ere ') . "( $sql )" : ''; /usr/share/perl5/Parse/RecDescent.pm: $lookahead = $lookah +ead ? -$lookahead : -1; /usr/share/perl5/Parse/RecDescent.pm: $lookahead = $lookah +ead ? $lookahead : 1; /usr/share/perl5/HTTP/Cookies/Netscape.pm: $expires = $expires ? $ +expires - $HTTP::Cookies::EPOCH_OFFSET : 0; /usr/share/perl5/HTTP/Cookies/Netscape.pm: $secure = $secure ? "TR +UE" : "FALSE"; /usr/share/perl5/Config/Tiny.pm: $encoding = $encoding ? "<:$en +coding" : '<'; /usr/share/perl5/Config/Tiny.pm: $encoding = $encoding ? ">:$en +coding" : '>'; /usr/share/perl5/Mojo/DOM.pm: $start = $start ? ($#$tree + 1) : _s +tart($tree); /usr/share/perl5/Mojo/DOM.pm: $offset = $offset ? $#$tree : 0; /usr/share/perl5/Font/TTF/OldMort.pm: $_ = $_ +? $_ - ($mappingTables / 2) : undef; /usr/share/perl5/Font/TTF/Mort/Contextual.pm: $_ = $_ ? $_ + - ($mappingTables / 2) : undef; /usr/share/perl5/Net/EmptyPort.pm: $proto = $proto ? lc($proto +) : 'tcp'; /usr/share/perl5/Net/EmptyPort.pm: $proto = $proto ? lc($proto +) : 'tcp'; /usr/share/perl5/Net/SNMP/Transport/IPv6.pm: $s = $s ? sprintf('%%% +u', $s) : q{}; /usr/share/perl5/Net/SNMP/Transport/IPv6.pm: $s = $s ? pack('N', $s +) : q{}; /usr/share/perl5/UNIVERSAL/isa.pm: $extra = $extra ? " ($extra)" : + ''; /usr/share/perl5/IO/Socket/Socks.pm: $status = $status ? AUTHREPLY +_SUCCESS : 1; #XXX AUTHREPLY_FAILURE broken /usr/share/perl5/Text/CSV_PP.pm: $v =~ m/^[0-9]/ or $v = $v ? +1 : 0; # default for true/false /usr/share/perl5/Text/CSV_PP.pm: $v =~ m/^[0-9]/ or $v = $v ? +1 : 0; # default for true/false /usr/share/perl5/Lintian/Tags.pm: $found = $found +? 0 : 1; /usr/share/perl5/Excel/Writer/XLSX/Drawing.pm: $underline = $under +line ? 'sng' : 'none'; /usr/share/perl5/Excel/Writer/XLSX/Drawing.pm: $strike = $strike ? + 'Strike' : 'noStrike'; /usr/share/perl5/Test/Toolbox.pm: $is = $is ? 'true' : 'false'; /usr/share/perl5/Test/Toolbox.pm: $should = $should ? 'true' : 'fa +lse'; /usr/share/perl5/Test/Toolbox.pm: $ok = $ok ? 1 : 0; /usr/share/perl5/Spreadsheet/WriteExcel/Worksheet.pm: $visible + = $visible ? 0x0000 : 0x0002; /usr/share/perl5/Spreadsheet/WriteExcel/Worksheet.pm: $visible + = $visible ? 0x0002 : 0x0000; /usr/share/perl5/Spreadsheet/ParseExcel/Utility.pm: $doubl +e_quote = $double_quote ? 0 : 1; /usr/share/perl5/Spreadsheet/XLSX/Utility2007.pm: $iDblQ = + $iDblQ? 0: 1; /usr/share/perl5/Zoidberg/StringParser.pm: $expr = $ex +pr ? '('.$expr.')|' : ''; /usr/share/perl5/Image/ExifTool/QuickTime.pm: $lang = $lang ? +"($lang) " : ''; /usr/share/perl5/Image/ExifTool/QuickTime.pm: $lang = $lan +g ? "($lang) " : ''; /usr/share/perl5/Image/ExifTool/QuickTime.pm: $lang = $lan +g ? "($lang) " : ''; /usr/share/perl5/Image/ExifTool/QuickTime.pm: $lang = $lan +g ? "($lang) " : ''; /usr/share/perl5/Image/ExifTool/QuickTime.pm: $lang = $lan +g ? "($lang) " : ''; /usr/share/perl5/Image/ExifTool/XMPStruct.pl: $delim = $delim +? "\\$delim|,|\\||\$" : ',|\\||$'; /usr/share/perl5/Image/ExifTool/BuildTagLookup.pm: $rowCla +ss = $rowClass ? '' : " class=b"; /usr/share/perl5/Image/ExifTool/ASF.pm: $_ = $_ ? 'True' : + 'False'; /usr/share/perl5/Image/ExifTool.pm: $tagInfo = $tagInfo ? { Name = +> $tagInfo } : { } unless ref $tagInfo eq 'HASH'; /usr/share/perl5/Type/Params.pm: $constraint = $constraint + ? Any : Optional[Any]; /usr/share/perl5/CGI/Compile.pm: $proto = $proto ? "($proto)" : '' +; /usr/share/perl5/assert.pl: $w = $w ? '@ = ' : '$ = '; /usr/share/perl5/IPC/Run.pm: $r = $r ? '' : " ERROR $!"; /usr/share/perl5/IPC/Run.pm: $out = $out ? 'b' : 'w' + if vec( $self->{WIN}, $_, 1 ); /usr/share/perl5/IPC/Run.pm: $out = $out ? uc( $out ) : + 'x' if vec( $self->{EIN}, $_, 1 ); /usr/share/perl5/IPC/Run.pm: $out = $out ? 'b' : 'w' + if vec( $self->{WOUT}, $_, 1 ); /usr/share/perl5/IPC/Run.pm: $out = $out ? uc( $out ) : + 'x' if vec( $self->{EOUT}, $_, 1 ); /usr/share/perl5/AppConfig/State.pm: $value = $value ? 0 : 1 i +f $negate; ./SQL/Translator/Producer/Oracle.pm: $index_name = $in +dex_name ? mk_name( $index_name ) ./SQL/Translator/Producer/Oracle.pm: $index_name = $in +dex_name ? mk_name( $index_name ) ./SQL/Translator/Producer/Oracle.pm: $index_name = $in +dex_name ? mk_name( $index_name ) ./SQL/Translator/Producer/Oracle.pm: $default = $defau +lt ? "'1'" : "'0'"; ./SQL/Abstract.pm: $sql = $sql ? $self->_sqlcase(' where ') . "( $sq +l )" : ''; ./Parse/RecDescent.pm: $lookahead = $lookahead ? -$lookahe +ad : -1; ./Parse/RecDescent.pm: $lookahead = $lookahead ? $lookahea +d : 1; ./HTTP/Cookies/Netscape.pm: $expires = $expires ? $expires - $HTTP +::Cookies::EPOCH_OFFSET : 0; ./HTTP/Cookies/Netscape.pm: $secure = $secure ? "TRUE" : "FALSE"; ./Config/Tiny.pm: $encoding = $encoding ? "<:$encoding" : '<'; ./Config/Tiny.pm: $encoding = $encoding ? ">:$encoding" : '>'; ./Mojo/DOM.pm: $start = $start ? ($#$tree + 1) : _start($tree); ./Mojo/DOM.pm: $offset = $offset ? $#$tree : 0; ./Font/TTF/OldMort.pm: $_ = $_ ? $_ - ($mappin +gTables / 2) : undef; ./Font/TTF/Mort/Contextual.pm: $_ = $_ ? $_ - ($mappingTab +les / 2) : undef; ./Net/EmptyPort.pm: $proto = $proto ? lc($proto) : 'tcp'; ./Net/EmptyPort.pm: $proto = $proto ? lc($proto) : 'tcp'; ./Net/SNMP/Transport/IPv6.pm: $s = $s ? sprintf('%%%u', $s) : q{}; ./Net/SNMP/Transport/IPv6.pm: $s = $s ? pack('N', $s) : q{}; ./UNIVERSAL/isa.pm: $extra = $extra ? " ($extra)" : ''; ./IO/Socket/Socks.pm: $status = $status ? AUTHREPLY_SUCCESS : 1; # +XXX AUTHREPLY_FAILURE broken ./Text/CSV_PP.pm: $v =~ m/^[0-9]/ or $v = $v ? 1 : 0; # defaul +t for true/false ./Text/CSV_PP.pm: $v =~ m/^[0-9]/ or $v = $v ? 1 : 0; # defaul +t for true/false ./Lintian/Tags.pm: $found = $found ? 0 : 1; ./Excel/Writer/XLSX/Drawing.pm: $underline = $underline ? 'sng' : +'none'; ./Excel/Writer/XLSX/Drawing.pm: $strike = $strike ? 'Strike' : 'no +Strike'; ./Test/Toolbox.pm: $is = $is ? 'true' : 'false'; ./Test/Toolbox.pm: $should = $should ? 'true' : 'false'; ./Test/Toolbox.pm: $ok = $ok ? 1 : 0; ./Spreadsheet/WriteExcel/Worksheet.pm: $visible = $visible + ? 0x0000 : 0x0002; ./Spreadsheet/WriteExcel/Worksheet.pm: $visible = $visible + ? 0x0002 : 0x0000; ./Spreadsheet/ParseExcel/Utility.pm: $double_quote = $doub +le_quote ? 0 : 1; ./Spreadsheet/XLSX/Utility2007.pm: $iDblQ = $iDblQ? 0: 1; ./Zoidberg/StringParser.pm: $expr = $expr ? '('.$expr. +')|' : ''; ./Image/ExifTool/QuickTime.pm: $lang = $lang ? "($lang) " : '' +; ./Image/ExifTool/QuickTime.pm: $lang = $lang ? "($lang) " +: ''; ./Image/ExifTool/QuickTime.pm: $lang = $lang ? "($lang) " +: ''; ./Image/ExifTool/QuickTime.pm: $lang = $lang ? "($lang) " +: ''; ./Image/ExifTool/QuickTime.pm: $lang = $lang ? "($lang) " +: ''; ./Image/ExifTool/XMPStruct.pl: $delim = $delim ? "\\$delim|,|\ +\||\$" : ',|\\||$'; ./Image/ExifTool/BuildTagLookup.pm: $rowClass = $rowClass +? '' : " class=b"; ./Image/ExifTool/ASF.pm: $_ = $_ ? 'True' : 'False'; ./Image/ExifTool.pm: $tagInfo = $tagInfo ? { Name => $tagInfo } : +{ } unless ref $tagInfo eq 'HASH'; ./Type/Params.pm: $constraint = $constraint ? Any : Option +al[Any]; ./CGI/Compile.pm: $proto = $proto ? "($proto)" : ''; ./assert.pl: $w = $w ? '@ = ' : '$ = '; ./IPC/Run.pm: $r = $r ? '' : " ERROR $!"; ./IPC/Run.pm: $out = $out ? 'b' : 'w' if vec( $s +elf->{WIN}, $_, 1 ); ./IPC/Run.pm: $out = $out ? uc( $out ) : 'x' if vec( $s +elf->{EIN}, $_, 1 ); ./IPC/Run.pm: $out = $out ? 'b' : 'w' if vec( $s +elf->{WOUT}, $_, 1 ); ./IPC/Run.pm: $out = $out ? uc( $out ) : 'x' if vec( $s +elf->{EOUT}, $_, 1 ); ./AppConfig/State.pm: $value = $value ? 0 : 1 if $negate;

      So, it looks like there are plenty of use cases ;)

      perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'
        So, it looks like there are plenty of use cases
        Just the .pm files in the perl core distribution contain over 700,000 lines. You show that those, combined with a bunch of 3rd party modules, contain only around 100 instances of code likely to be able to make use of this proposed operator. If anything I think you've shown that this is a very rare use case and hardly justifies its addition to core.

        Dave.

        So, it looks like there are plenty of use cases ;)

        Iff you dont need backwards compatibility

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