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package Sub::Middler; |
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use 5.024000; |
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use strict; |
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use warnings; |
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use feature "refaliasing"; |
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our $VERSION = 'v0.2.0'; |
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sub new { |
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#simply an array... |
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bless [], __PACKAGE__; |
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} |
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# register sub refs to middleware makers |
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sub register { |
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no warnings "experimental"; |
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\my @middleware=$_[0]; #self |
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my $sub=$_[1]; |
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die "Middleware must be a CODE reference" unless ref($sub) eq "CODE"; |
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push @middleware, $sub; |
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return $_[0]; #allow chaining |
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} |
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*append=\®ister; |
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*add=\®ister; |
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# Link together sub and give each one an index |
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# Required argument is the 'dispatcher' which is the end point to call |
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# |
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sub link { |
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no warnings "experimental"; |
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die "A CODE reference is requred when linking middleware" unless(@_ >=2 and ref $_[1] eq "CODE"); |
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\my @middleware=shift; #self; |
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my $dispatcher=shift; |
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my @args=@_; |
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my @mw; # The generated subs |
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for my $i (reverse 0..@middleware-1){ |
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my $maker=$middleware[$i]; |
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my $next=($i==@middleware-1)?$dispatcher:$mw[$i+1]; |
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$mw[$i]=$maker->($next, $i, @args); |
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} |
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@middleware?$mw[0]:$dispatcher; |
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} |
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1; |
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=head1 NAME |
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Sub::Middler - Middleware subroutine chaining |
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=head1 SYNOPSIS |
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use strict; |
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use warnings; |
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use Sub::Middler; |
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my $middler=Sub::Middler->new; |
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71
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$middler->register(mw1(x=>1)); |
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$middler->register(mw2(y=>10)); |
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74
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my $head=$middler->link( |
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sub { |
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print "Result: $_[0]\n"; |
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} |
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); |
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$head->(0); # Call the Chain |
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# Middleware 1 |
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sub mw1 { |
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my %options=@_; |
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sub { |
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my ($next, $index, @optional)=@_; |
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sub { |
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my $work=$_[0]+$options{x}; |
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$next->($work); |
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} |
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} |
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} |
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# Middleware 2 |
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sub mw2 { |
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my %options=@_; |
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sub { |
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my ($next, $index, @optional)=@_; |
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sub { |
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my $work= $_[0]*$options{y}; |
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$next->( $work); |
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} |
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} |
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} |
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106
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=head1 DESCRIPTION |
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A small module, facilitating linking together subroutines, acting as middleware |
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or filters into chains with low runtime overhead. |
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To achieve this, the 'complexity' is offloaded to the definition of |
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middleware/filters subroutines. They must be wrapped in subroutines |
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appropriately to facilitate the lexical binding of linking variables. |
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This differs from other 'sub chaining' modules as it does not use a loop |
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internally to iterate over a list of subroutines at runtime. As such there is |
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no implicit call to the 'next' item in the chain. Each stage can run the |
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following stage synchronously or asynchronously or not at all. Each element in |
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the chain is responsible for how and when it calls the 'next'. |
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Finally the arguments and signatures of each stage of middleware are completely |
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user defined and are not interfered with by this module. This allows reuse of |
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the C<@_> array in calling subsequent stages for ultimate performance if you |
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know what you're doing. |
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127
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=head1 API |
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129
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=head2 Managing a chain |
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=head3 new |
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133
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my $object=Sub::Middler->new; |
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Creates a empty middler object ready to accept middleware. The object is a |
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blessed array reference which stores the middleware directly. |
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138
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=head3 register |
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$object->register(my_middlware()); |
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Appends the middleware to the internal list for later linking. |
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=head3 append, add |
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Alias for register |
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148
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=head3 link |
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150
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$object->link($last,[@args]); |
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152
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Links together the registered middleware in the sequence of addition. Each |
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middleware is intrinsically linked to the next middleware in the list. The last |
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middleware being linked to the C<$last> argument, which must be a code ref. |
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156
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The C<$last> ref MUST be a regular subroutine reference, acting as the |
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'kernel' as described in following sections. |
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159
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Calls C if C<$last> is not a code ref. |
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161
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Any optional additional arguments C<@args> are passed to this function are |
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passed on to each 'maker' sub after the C<$next> and C<$index>, parameters. |
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This gives an alternative approach to distributing configuration data to each |
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item in the chain prior to runtime. It is up to each item's maker sub to store |
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relevant passed values as they see fit. |
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167
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=head2 Creating Middleware |
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To achieve low over head in linking middleware, functional programming |
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techniques (higher order functions) are utilised. This also give the greatest |
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flexibility to the middleware, as signatures are completely user defined. |
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The trade off is that the middleware must be defined in a certain code |
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structure. While this isn't difficult, it takes a minute to wrap your head |
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around. |
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177
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178
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=head3 Middlware Definition |
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Middleware must be a subroutine (top/name) which returns a anonymous subroutine |
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(maker), which also returns a anonymous subroutine to perform work (kernel). |
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183
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This sounds complicated by this is what is looks like in code: |
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185
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sub my_middleware { (1) Top/name subroutine |
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my %options=@_; Store any config |
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188
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sub { (2) maker sub is returned |
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my ($next, $index, @optional)=@_; (3) Must store at least $next |
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191
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sub { (4) Returns the kernel sub |
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# Code here implements your middleware |
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# %options are lexically accessable here |
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# as are the @optional parameters |
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196
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197
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# Execute the next item in the chain |
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$next->(...); (5) Does work and calls the next entry |
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200
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201
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(6) Post work if applicable |
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} |
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} |
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} |
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206
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=over |
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208
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=item Top Subroutine |
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210
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The top sub routine (1) can take any arguments you desire and can be called |
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what you like. The idea is it represents your middleware/filter and stores any |
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setup lexically for the B sub to close over. It returns the B |
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sub. |
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215
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=item Maker Subroutine |
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217
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This anonymous sub (2) closes over the variables stored in B and is the |
218
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input to this module (via C). When being linked (called) by this |
219
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module it is provided at least two arguments: the reference to the next item in |
220
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the chain and the current middleware index. These B be stored to be |
221
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useful, but can be called anything you like (3). |
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223
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Any optional/additional arguments supplied during a call to C are also |
224
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used as arguments 'as is' to all maker subroutines in the chain. |
225
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226
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227
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=item Kernel subroutine |
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229
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This anonymous subroutine (4) actually performs the work of the |
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middleware/filter. After work is done, the next item in the chain must be |
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called explicitly (5). This supports synchronous or asynchronous middleware. |
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Any extra work can be performed after the chain is completed after this call |
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(6). |
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=back |
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=head2 LINKING CHAINS |
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Multiple chains of middleware can be linked together. This needs to be done in |
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reverse order. The last chain after being linked, becomes the C<$last> item |
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when linking the preceding chain and so on. |
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=head2 EXAMPLES |
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The synopsis example can be found in the examples directory of this |
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distribution. |
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=head1 SEE ALSO |
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L and L links together subs. They provide other |
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features that this module does not. |
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These iterate over a list of subroutines at runtime to achieve named subs etc. |
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where as this module pre links subroutines together, reducing overhead. |
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=head1 AUTHOR |
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Ruben Westerberg, Edrclaw@mac.comE |
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=head1 REPOSITORTY and BUGS |
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Please report any bugs via git hub: L |
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=head1 COPYRIGHT AND LICENSE |
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Copyright (C) 2023 by Ruben Westerberg |
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This library is free software; you can redistribute it |
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and/or modify it under the same terms as Perl or the MIT |
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license. |
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=head1 DISCLAIMER OF WARRANTIES |
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THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS |
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OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE |
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A |
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PARTICULAR PURPOSE. |
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=cut |
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