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Diffstat (limited to 'Master/tlpkg/tlperl/site/lib/Try')
-rw-r--r-- | Master/tlpkg/tlperl/site/lib/Try/Tiny.pm | 804 |
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diff --git a/Master/tlpkg/tlperl/site/lib/Try/Tiny.pm b/Master/tlpkg/tlperl/site/lib/Try/Tiny.pm new file mode 100644 index 00000000000..476a215fe39 --- /dev/null +++ b/Master/tlpkg/tlperl/site/lib/Try/Tiny.pm @@ -0,0 +1,804 @@ +package Try::Tiny; # git description: v0.27-8-g8dc27c7 +use 5.006; +# ABSTRACT: Minimal try/catch with proper preservation of $@ + +our $VERSION = '0.28'; + +use strict; +use warnings; + +use Exporter 5.57 'import'; +our @EXPORT = our @EXPORT_OK = qw(try catch finally); + +use Carp; +$Carp::Internal{+__PACKAGE__}++; + +BEGIN { + my $su = $INC{'Sub/Util.pm'} && defined &Sub::Util::set_subname; + my $sn = $INC{'Sub/Name.pm'} && eval { Sub::Name->VERSION(0.08) }; + unless ($su || $sn) { + $su = eval { require Sub::Util; } && defined &Sub::Util::set_subname; + unless ($su) { + $sn = eval { require Sub::Name; Sub::Name->VERSION(0.08) }; + } + } + + *_subname = $su ? \&Sub::Util::set_subname + : $sn ? \&Sub::Name::subname + : sub { $_[1] }; + *_HAS_SUBNAME = ($su || $sn) ? sub(){1} : sub(){0}; +} + +my %_finally_guards; + +# Need to prototype as @ not $$ because of the way Perl evaluates the prototype. +# Keeping it at $$ means you only ever get 1 sub because we need to eval in a list +# context & not a scalar one + +sub try (&;@) { + my ( $try, @code_refs ) = @_; + + # we need to save this here, the eval block will be in scalar context due + # to $failed + my $wantarray = wantarray; + + # work around perl bug by explicitly initializing these, due to the likelyhood + # this will be used in global destruction (perl rt#119311) + my ( $catch, @finally ) = (); + + # find labeled blocks in the argument list. + # catch and finally tag the blocks by blessing a scalar reference to them. + foreach my $code_ref (@code_refs) { + + if ( ref($code_ref) eq 'Try::Tiny::Catch' ) { + croak 'A try() may not be followed by multiple catch() blocks' + if $catch; + $catch = ${$code_ref}; + } elsif ( ref($code_ref) eq 'Try::Tiny::Finally' ) { + push @finally, ${$code_ref}; + } else { + croak( + 'try() encountered an unexpected argument (' + . ( defined $code_ref ? $code_ref : 'undef' ) + . ') - perhaps a missing semi-colon before or' + ); + } + } + + # FIXME consider using local $SIG{__DIE__} to accumulate all errors. It's + # not perfect, but we could provide a list of additional errors for + # $catch->(); + + # name the blocks if we have Sub::Name installed + my $caller = caller; + _subname("${caller}::try {...} " => $try) + if _HAS_SUBNAME; + + # set up scope guards to invoke the finally blocks at the end. + # this should really be a function scope lexical variable instead of + # file scope + local but that causes issues with perls < 5.20 due to + # perl rt#119311 + local $_finally_guards{guards} = [ + map { Try::Tiny::ScopeGuard->_new($_) } + @finally + ]; + + # save the value of $@ so we can set $@ back to it in the beginning of the eval + # and restore $@ after the eval finishes + my $prev_error = $@; + + my ( @ret, $error ); + + # failed will be true if the eval dies, because 1 will not be returned + # from the eval body + my $failed = not eval { + $@ = $prev_error; + + # evaluate the try block in the correct context + if ( $wantarray ) { + @ret = $try->(); + } elsif ( defined $wantarray ) { + $ret[0] = $try->(); + } else { + $try->(); + }; + + return 1; # properly set $failed to false + }; + + # preserve the current error and reset the original value of $@ + $error = $@; + $@ = $prev_error; + + # at this point $failed contains a true value if the eval died, even if some + # destructor overwrote $@ as the eval was unwinding. + if ( $failed ) { + # pass $error to the finally blocks + push @$_, $error for @{$_finally_guards{guards}}; + + # if we got an error, invoke the catch block. + if ( $catch ) { + # This works like given($error), but is backwards compatible and + # sets $_ in the dynamic scope for the body of C<$catch> + for ($error) { + return $catch->($error); + } + + # in case when() was used without an explicit return, the C<for> + # loop will be aborted and there's no useful return value + } + + return; + } else { + # no failure, $@ is back to what it was, everything is fine + return $wantarray ? @ret : $ret[0]; + } +} + +sub catch (&;@) { + my ( $block, @rest ) = @_; + + croak 'Useless bare catch()' unless wantarray; + + my $caller = caller; + _subname("${caller}::catch {...} " => $block) + if _HAS_SUBNAME; + return ( + bless(\$block, 'Try::Tiny::Catch'), + @rest, + ); +} + +sub finally (&;@) { + my ( $block, @rest ) = @_; + + croak 'Useless bare finally()' unless wantarray; + + my $caller = caller; + _subname("${caller}::finally {...} " => $block) + if _HAS_SUBNAME; + return ( + bless(\$block, 'Try::Tiny::Finally'), + @rest, + ); +} + +{ + package # hide from PAUSE + Try::Tiny::ScopeGuard; + + use constant UNSTABLE_DOLLARAT => ("$]" < '5.013002') ? 1 : 0; + + sub _new { + shift; + bless [ @_ ]; + } + + sub DESTROY { + my ($code, @args) = @{ $_[0] }; + + local $@ if UNSTABLE_DOLLARAT; + eval { + $code->(@args); + 1; + } or do { + warn + "Execution of finally() block $code resulted in an exception, which " + . '*CAN NOT BE PROPAGATED* due to fundamental limitations of Perl. ' + . 'Your program will continue as if this event never took place. ' + . "Original exception text follows:\n\n" + . (defined $@ ? $@ : '$@ left undefined...') + . "\n" + ; + } + } +} + +__PACKAGE__ + +__END__ + +=pod + +=encoding UTF-8 + +=head1 NAME + +Try::Tiny - Minimal try/catch with proper preservation of $@ + +=head1 VERSION + +version 0.28 + +=head1 SYNOPSIS + +You can use Try::Tiny's C<try> and C<catch> to expect and handle exceptional +conditions, avoiding quirks in Perl and common mistakes: + + # handle errors with a catch handler + try { + die "foo"; + } catch { + warn "caught error: $_"; # not $@ + }; + +You can also use it like a standalone C<eval> to catch and ignore any error +conditions. Obviously, this is an extreme measure not to be undertaken +lightly: + + # just silence errors + try { + die "foo"; + }; + +=head1 DESCRIPTION + +This module provides bare bones C<try>/C<catch>/C<finally> statements that are designed to +minimize common mistakes with eval blocks, and NOTHING else. + +This is unlike L<TryCatch> which provides a nice syntax and avoids adding +another call stack layer, and supports calling C<return> from the C<try> block to +return from the parent subroutine. These extra features come at a cost of a few +dependencies, namely L<Devel::Declare> and L<Scope::Upper> which are +occasionally problematic, and the additional catch filtering uses L<Moose> +type constraints which may not be desirable either. + +The main focus of this module is to provide simple and reliable error handling +for those having a hard time installing L<TryCatch>, but who still want to +write correct C<eval> blocks without 5 lines of boilerplate each time. + +It's designed to work as correctly as possible in light of the various +pathological edge cases (see L</BACKGROUND>) and to be compatible with any style +of error values (simple strings, references, objects, overloaded objects, etc). + +If the C<try> block dies, it returns the value of the last statement executed in +the C<catch> block, if there is one. Otherwise, it returns C<undef> in scalar +context or the empty list in list context. The following examples all +assign C<"bar"> to C<$x>: + + my $x = try { die "foo" } catch { "bar" }; + my $x = try { die "foo" } || "bar"; + my $x = (try { die "foo" }) // "bar"; + + my $x = eval { die "foo" } || "bar"; + +You can add C<finally> blocks, yielding the following: + + my $x; + try { die 'foo' } finally { $x = 'bar' }; + try { die 'foo' } catch { warn "Got a die: $_" } finally { $x = 'bar' }; + +C<finally> blocks are always executed making them suitable for cleanup code +which cannot be handled using local. You can add as many C<finally> blocks to a +given C<try> block as you like. + +Note that adding a C<finally> block without a preceding C<catch> block +suppresses any errors. This behaviour is consistent with using a standalone +C<eval>, but it is not consistent with C<try>/C<finally> patterns found in +other programming languages, such as Java, Python, Javascript or C#. If you +learnt the C<try>/C<finally> pattern from one of these languages, watch out for +this. + +=head1 EXPORTS + +All functions are exported by default using L<Exporter>. + +If you need to rename the C<try>, C<catch> or C<finally> keyword consider using +L<Sub::Import> to get L<Sub::Exporter>'s flexibility. + +=over 4 + +=item try (&;@) + +Takes one mandatory C<try> subroutine, an optional C<catch> subroutine and C<finally> +subroutine. + +The mandatory subroutine is evaluated in the context of an C<eval> block. + +If no error occurred the value from the first block is returned, preserving +list/scalar context. + +If there was an error and the second subroutine was given it will be invoked +with the error in C<$_> (localized) and as that block's first and only +argument. + +C<$@> does B<not> contain the error. Inside the C<catch> block it has the same +value it had before the C<try> block was executed. + +Note that the error may be false, but if that happens the C<catch> block will +still be invoked. + +Once all execution is finished then the C<finally> block, if given, will execute. + +=item catch (&;@) + +Intended to be used in the second argument position of C<try>. + +Returns a reference to the subroutine it was given but blessed as +C<Try::Tiny::Catch> which allows try to decode correctly what to do +with this code reference. + + catch { ... } + +Inside the C<catch> block the caught error is stored in C<$_>, while previous +value of C<$@> is still available for use. This value may or may not be +meaningful depending on what happened before the C<try>, but it might be a good +idea to preserve it in an error stack. + +For code that captures C<$@> when throwing new errors (i.e. +L<Class::Throwable>), you'll need to do: + + local $@ = $_; + +=item finally (&;@) + + try { ... } + catch { ... } + finally { ... }; + +Or + + try { ... } + finally { ... }; + +Or even + + try { ... } + finally { ... } + catch { ... }; + +Intended to be the second or third element of C<try>. C<finally> blocks are always +executed in the event of a successful C<try> or if C<catch> is run. This allows +you to locate cleanup code which cannot be done via C<local()> e.g. closing a file +handle. + +When invoked, the C<finally> block is passed the error that was caught. If no +error was caught, it is passed nothing. (Note that the C<finally> block does not +localize C<$_> with the error, since unlike in a C<catch> block, there is no way +to know if C<$_ == undef> implies that there were no errors.) In other words, +the following code does just what you would expect: + + try { + die_sometimes(); + } catch { + # ...code run in case of error + } finally { + if (@_) { + print "The try block died with: @_\n"; + } else { + print "The try block ran without error.\n"; + } + }; + +B<You must always do your own error handling in the C<finally> block>. C<Try::Tiny> will +not do anything about handling possible errors coming from code located in these +blocks. + +Furthermore B<exceptions in C<finally> blocks are not trappable and are unable +to influence the execution of your program>. This is due to limitation of +C<DESTROY>-based scope guards, which C<finally> is implemented on top of. This +may change in a future version of Try::Tiny. + +In the same way C<catch()> blesses the code reference this subroutine does the same +except it bless them as C<Try::Tiny::Finally>. + +=back + +=head1 BACKGROUND + +There are a number of issues with C<eval>. + +=head2 Clobbering $@ + +When you run an C<eval> block and it succeeds, C<$@> will be cleared, potentially +clobbering an error that is currently being caught. + +This causes action at a distance, clearing previous errors your caller may have +not yet handled. + +C<$@> must be properly localized before invoking C<eval> in order to avoid this +issue. + +More specifically, C<$@> is clobbered at the beginning of the C<eval>, which +also makes it impossible to capture the previous error before you die (for +instance when making exception objects with error stacks). + +For this reason C<try> will actually set C<$@> to its previous value (the one +available before entering the C<try> block) in the beginning of the C<eval> +block. + +=head2 Localizing $@ silently masks errors + +Inside an C<eval> block, C<die> behaves sort of like: + + sub die { + $@ = $_[0]; + return_undef_from_eval(); + } + +This means that if you were polite and localized C<$@> you can't die in that +scope, or your error will be discarded (printing "Something's wrong" instead). + +The workaround is very ugly: + + my $error = do { + local $@; + eval { ... }; + $@; + }; + + ... + die $error; + +=head2 $@ might not be a true value + +This code is wrong: + + if ( $@ ) { + ... + } + +because due to the previous caveats it may have been unset. + +C<$@> could also be an overloaded error object that evaluates to false, but +that's asking for trouble anyway. + +The classic failure mode is: + + sub Object::DESTROY { + eval { ... } + } + + eval { + my $obj = Object->new; + + die "foo"; + }; + + if ( $@ ) { + + } + +In this case since C<Object::DESTROY> is not localizing C<$@> but still uses +C<eval>, it will set C<$@> to C<"">. + +The destructor is called when the stack is unwound, after C<die> sets C<$@> to +C<"foo at Foo.pm line 42\n">, so by the time C<if ( $@ )> is evaluated it has +been cleared by C<eval> in the destructor. + +The workaround for this is even uglier than the previous ones. Even though we +can't save the value of C<$@> from code that doesn't localize, we can at least +be sure the C<eval> was aborted due to an error: + + my $failed = not eval { + ... + + return 1; + }; + +This is because an C<eval> that caught a C<die> will always return a false +value. + +=head1 SHINY SYNTAX + +Using Perl 5.10 you can use L<perlsyn/"Switch statements">. + +=for stopwords topicalizer + +The C<catch> block is invoked in a topicalizer context (like a C<given> block), +but note that you can't return a useful value from C<catch> using the C<when> +blocks without an explicit C<return>. + +This is somewhat similar to Perl 6's C<CATCH> blocks. You can use it to +concisely match errors: + + try { + require Foo; + } catch { + when (/^Can't locate .*?\.pm in \@INC/) { } # ignore + default { die $_ } + }; + +=head1 CAVEATS + +=over 4 + +=item * + +C<@_> is not available within the C<try> block, so you need to copy your +argument list. In case you want to work with argument values directly via C<@_> +aliasing (i.e. allow C<$_[1] = "foo">), you need to pass C<@_> by reference: + + sub foo { + my ( $self, @args ) = @_; + try { $self->bar(@args) } + } + +or + + sub bar_in_place { + my $self = shift; + my $args = \@_; + try { $_ = $self->bar($_) for @$args } + } + +=item * + +C<return> returns from the C<try> block, not from the parent sub (note that +this is also how C<eval> works, but not how L<TryCatch> works): + + sub parent_sub { + try { + die; + } + catch { + return; + }; + + say "this text WILL be displayed, even though an exception is thrown"; + } + +Instead, you should capture the return value: + + sub parent_sub { + my $success = try { + die; + 1; + }; + return unless $success; + + say "This text WILL NEVER appear!"; + } + # OR + sub parent_sub_with_catch { + my $success = try { + die; + 1; + } + catch { + # do something with $_ + return undef; #see note + }; + return unless $success; + + say "This text WILL NEVER appear!"; + } + +Note that if you have a C<catch> block, it must return C<undef> for this to work, +since if a C<catch> block exists, its return value is returned in place of C<undef> +when an exception is thrown. + +=item * + +C<try> introduces another caller stack frame. L<Sub::Uplevel> is not used. L<Carp> +will not report this when using full stack traces, though, because +C<%Carp::Internal> is used. This lack of magic is considered a feature. + +=for stopwords unhygienically + +=item * + +The value of C<$_> in the C<catch> block is not guaranteed to be the value of +the exception thrown (C<$@>) in the C<try> block. There is no safe way to +ensure this, since C<eval> may be used unhygienically in destructors. The only +guarantee is that the C<catch> will be called if an exception is thrown. + +=item * + +The return value of the C<catch> block is not ignored, so if testing the result +of the expression for truth on success, be sure to return a false value from +the C<catch> block: + + my $obj = try { + MightFail->new; + } catch { + ... + + return; # avoid returning a true value; + }; + + return unless $obj; + +=item * + +C<$SIG{__DIE__}> is still in effect. + +Though it can be argued that C<$SIG{__DIE__}> should be disabled inside of +C<eval> blocks, since it isn't people have grown to rely on it. Therefore in +the interests of compatibility, C<try> does not disable C<$SIG{__DIE__}> for +the scope of the error throwing code. + +=item * + +Lexical C<$_> may override the one set by C<catch>. + +For example Perl 5.10's C<given> form uses a lexical C<$_>, creating some +confusing behavior: + + given ($foo) { + when (...) { + try { + ... + } catch { + warn $_; # will print $foo, not the error + warn $_[0]; # instead, get the error like this + } + } + } + +Note that this behavior was changed once again in L<Perl5 version 18 +|https://metacpan.org/module/perldelta#given-now-aliases-the-global-_>. +However, since the entirety of lexical C<$_> is now L<considered experimental +|https://metacpan.org/module/perldelta#Lexical-_-is-now-experimental>, it +is unclear whether the new version 18 behavior is final. + +=back + +=head1 SEE ALSO + +=over 4 + +=item L<TryCatch> + +Much more feature complete, more convenient semantics, but at the cost of +implementation complexity. + +=item L<autodie> + +Automatic error throwing for builtin functions and more. Also designed to +work well with C<given>/C<when>. + +=item L<Throwable> + +A lightweight role for rolling your own exception classes. + +=item L<Error> + +Exception object implementation with a C<try> statement. Does not localize +C<$@>. + +=item L<Exception::Class::TryCatch> + +Provides a C<catch> statement, but properly calling C<eval> is your +responsibility. + +The C<try> keyword pushes C<$@> onto an error stack, avoiding some of the +issues with C<$@>, but you still need to localize to prevent clobbering. + +=back + +=head1 LIGHTNING TALK + +I gave a lightning talk about this module, you can see the slides (Firefox +only): + +L<http://web.archive.org/web/20100628040134/http://nothingmuch.woobling.org/talks/takahashi.xul> + +Or read the source: + +L<http://web.archive.org/web/20100305133605/http://nothingmuch.woobling.org/talks/yapc_asia_2009/try_tiny.yml> + +=head1 SUPPORT + +Bugs may be submitted through L<the RT bug tracker|https://rt.cpan.org/Public/Dist/Display.html?Name=Try-Tiny> +(or L<bug-Try-Tiny@rt.cpan.org|mailto:bug-Try-Tiny@rt.cpan.org>). + +=head1 AUTHORS + +=over 4 + +=item * + +יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org> + +=item * + +Jesse Luehrs <doy@tozt.net> + +=back + +=head1 CONTRIBUTORS + +=for stopwords Karen Etheridge Peter Rabbitson Ricardo Signes Mark Fowler Graham Knop Lukas Mai Dagfinn Ilmari Mannsåker Paul Howarth Rudolf Leermakers anaxagoras awalker chromatic Alex cm-perl Andrew Yates David Lowe Glenn Hans Dieter Pearcey Jonathan Yu Marc Mims Stosberg Pali + +=over 4 + +=item * + +Karen Etheridge <ether@cpan.org> + +=item * + +Peter Rabbitson <ribasushi@cpan.org> + +=item * + +Ricardo Signes <rjbs@cpan.org> + +=item * + +Mark Fowler <mark@twoshortplanks.com> + +=item * + +Graham Knop <haarg@haarg.org> + +=item * + +Lukas Mai <l.mai@web.de> + +=item * + +Dagfinn Ilmari Mannsåker <ilmari@ilmari.org> + +=item * + +Paul Howarth <paul@city-fan.org> + +=item * + +Rudolf Leermakers <rudolf@hatsuseno.org> + +=item * + +anaxagoras <walkeraj@gmail.com> + +=item * + +awalker <awalker@sourcefire.com> + +=item * + +chromatic <chromatic@wgz.org> + +=item * + +Alex <alex@koban.(none)> + +=item * + +cm-perl <cm-perl@users.noreply.github.com> + +=item * + +Andrew Yates <ayates@haddock.local> + +=item * + +David Lowe <davidl@lokku.com> + +=item * + +Glenn Fowler <cebjyre@cpan.org> + +=item * + +Hans Dieter Pearcey <hdp@weftsoar.net> + +=item * + +Jonathan Yu <JAWNSY@cpan.org> + +=item * + +Marc Mims <marc@questright.com> + +=item * + +Mark Stosberg <mark@stosberg.com> + +=item * + +Pali <pali@cpan.org> + +=back + +=head1 COPYRIGHT AND LICENCE + +This software is Copyright (c) 2009 by יובל קוג'מן (Yuval Kogman). + +This is free software, licensed under: + + The MIT (X11) License + +=cut |