Coding Gotchas

This page documents coding "gotchas" where things might not turn out how you expect them to.

Dreamwidth specific gotchas

LJ::Entry->new always returns an LJ::Entry

You might expect that given an invalid ditemid, you might get an undefined value back--but that is not the case. This is for efficiency's sake--entry and comment fetch requests are cached, and then when one of the entries is accessed (such as $entry->subject), all the entries or comments are requested all at once. Check the $entry->valid sub instead.

my $entry = LJ::Entry->new( $u, ditemid => $deleted_ditemid );
print "Entry 1 is defined\n" if defined $entry;
# use this instead of checking if the entry is defined
print "Entry 1 is valid\n" if defined $entry->valid;
 
$entry = LJ::Entry->new( $u, ditemid => $valid_ditemid );
print "Entry 2 is defined\n" if defined $entry;
print "Entry 2 is valid\n" if defined $entry->valid;

Returns

Invalid language.

You need to specify a language like this: <source lang="html4strict">...</source>

Supported languages for syntax highlighting:

4cs, 6502acme, 6502kickass, 6502tasm, 68000devpac, abap, actionscript, actionscript3, ada, algol68, apache, applescript, apt_sources, arm, asm, asp, asymptote, autoconf, autohotkey, autoit, avisynth, awk, bascomavr, bash, basic4gl, bf, bibtex, blitzbasic, bnf, boo, c, c_loadrunner, c_mac, caddcl, cadlisp, cfdg, cfm, chaiscript, cil, clojure, cmake, cobol, coffeescript, cpp, cpp-qt, csharp, css, cuesheet, d, dcl, dcpu16, dcs, delphi, diff, div, dos, dot, e, ecmascript, eiffel, email, epc, erlang, euphoria, f1, falcon, fo, fortran, freebasic, freeswitch, fsharp, gambas, gdb, genero, genie, gettext, glsl, gml, gnuplot, go, groovy, gwbasic, haskell, haxe, hicest, hq9plus, html4strict, html5, icon, idl, ini, inno, intercal, io, j, java, java5, javascript, jquery, kixtart, klonec, klonecpp, latex, lb, ldif, lisp, llvm, locobasic, logtalk, lolcode, lotusformulas, lotusscript, lscript, lsl2, lua, m68k, magiksf, make, mapbasic, matlab, mirc, mmix, modula2, modula3, mpasm, mxml, mysql, nagios, netrexx, newlisp, nsis, oberon2, objc, objeck, ocaml, ocaml-brief, octave, oobas, oorexx, oracle11, oracle8, oxygene, oz, parasail, parigp, pascal, pcre, per, perl, perl6, pf, php, php-brief, pic16, pike, pixelbender, pli, plsql, postgresql, povray, powerbuilder, powershell, proftpd, progress, prolog, properties, providex, purebasic, pycon, pys60, python, q, qbasic, rails, rebol, reg, rexx, robots, rpmspec, rsplus, ruby, s2, sas, scala, scheme, scilab, sdlbasic, smalltalk, smarty, spark, sparql, sql, stonescript, systemverilog, tcl, teraterm, text, thinbasic, tsql, typoscript, unicon, upc, urbi, uscript, vala, vb, vbnet, vedit, verilog, vhdl, vim, visualfoxpro, visualprolog, whitespace, whois, winbatch, xbasic, xml, xorg_conf, xpp, yaml, z80, zxbasic

Entry 1 is defined
Entry 2 is defined
Entry 2 is valid

$r->OK is 0

$r->OK is 0, not 200

General Perl gotchas

You can modify ...

use strict;
 
my $x;
 
print "x is '$x'\n";
foo($x);
print "x is now '$x'\n";
 
sub foo { $_[0] = "bar"; }

Returns

Invalid language.

You need to specify a language like this: <source lang="html4strict">...</source>

Supported languages for syntax highlighting:

4cs, 6502acme, 6502kickass, 6502tasm, 68000devpac, abap, actionscript, actionscript3, ada, algol68, apache, applescript, apt_sources, arm, asm, asp, asymptote, autoconf, autohotkey, autoit, avisynth, awk, bascomavr, bash, basic4gl, bf, bibtex, blitzbasic, bnf, boo, c, c_loadrunner, c_mac, caddcl, cadlisp, cfdg, cfm, chaiscript, cil, clojure, cmake, cobol, coffeescript, cpp, cpp-qt, csharp, css, cuesheet, d, dcl, dcpu16, dcs, delphi, diff, div, dos, dot, e, ecmascript, eiffel, email, epc, erlang, euphoria, f1, falcon, fo, fortran, freebasic, freeswitch, fsharp, gambas, gdb, genero, genie, gettext, glsl, gml, gnuplot, go, groovy, gwbasic, haskell, haxe, hicest, hq9plus, html4strict, html5, icon, idl, ini, inno, intercal, io, j, java, java5, javascript, jquery, kixtart, klonec, klonecpp, latex, lb, ldif, lisp, llvm, locobasic, logtalk, lolcode, lotusformulas, lotusscript, lscript, lsl2, lua, m68k, magiksf, make, mapbasic, matlab, mirc, mmix, modula2, modula3, mpasm, mxml, mysql, nagios, netrexx, newlisp, nsis, oberon2, objc, objeck, ocaml, ocaml-brief, octave, oobas, oorexx, oracle11, oracle8, oxygene, oz, parasail, parigp, pascal, pcre, per, perl, perl6, pf, php, php-brief, pic16, pike, pixelbender, pli, plsql, postgresql, povray, powerbuilder, powershell, proftpd, progress, prolog, properties, providex, purebasic, pycon, pys60, python, q, qbasic, rails, rebol, reg, rexx, robots, rpmspec, rsplus, ruby, s2, sas, scala, scheme, scilab, sdlbasic, smalltalk, smarty, spark, sparql, sql, stonescript, systemverilog, tcl, teraterm, text, thinbasic, tsql, typoscript, unicon, upc, urbi, uscript, vala, vb, vbnet, vedit, verilog, vhdl, vim, visualfoxpro, visualprolog, whitespace, whois, winbatch, xbasic, xml, xorg_conf, xpp, yaml, z80, zxbasic

x is ''
x is now 'bar'

use strict + my $foo if

use strict;
 
my $x = -1 if 0; # intentional false, for example.
$x = 1; # This accesses a *global, persistent across requests* $x

The condition can be anything, and this bug only happens if the "my $x" line does not execute because of the condition, if the condition is true then it will end up using the local as expected.

strict does not complain about this.

Do the following instead:

use strict;
 
my $x;
$x = -1 if 0;
$x = 1;