Difference between revisions of "Coding Gotchas"
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== General Perl gotchas == | == General Perl gotchas == | ||
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Revision as of 21:04, 8 March 2011
This page documents coding "gotchas" where things might not turn out how you expect them to.
Contents
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 change the external value of non-reference scalars passed to a subroutine
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;
