Action basics

Actions are the cornerstone of the ExtUtils::Builder framework. They provide an interface between build tools (e.g. ExtUtils::MakeMaker, Module::Build, ...) and building extensions. This allows producing and consuming sides to be completely independent from each other. It is a flexible abstraction around pieces of work, this work can be a piece of perl code, an external command, a mix of those or possibly other things.

An action can be consumed in many ways.

• execute(%args)

  This is often the simplest way of dealing with an action. It simple performs the action immediately, and will throw an exception on failure.

• to_command(%opts)

  This converts the action into a list of commands to be executed. The elements of this list are arrayrefs to that can each be executed using along these lines:

   for my $command ($work->to_command) {
     system(@$command);
   }
      

  It can take two optional named arguments: "perl" for the path to perl, and "config" for an ExtUtils::Config object used the find the current perl.

• to_code()

  This converts the action into a list of strings to be "eval"ed in order to execute them. This can be useful when you want to serialize the work that is to be done but don't want to force it to shell out.

• to_code_hash()

  This converts the action into a hash that can be used to create a new ExtUtils::Builder::Action::Code.

• flatten()

  This will return all primitive actions involved in this action. It may return $self, it may return an empty list. On composite actions, "flatten" can be called to retrieve the constituent actions, "flatten" is guaranteed to only return primitive actions.

• preference(@options)

  If a consumer can consume actions in more than one way, the "preference" method can be used to choose between options. This function expects a list of options out of "code", "command", "execute" and "flatten". You probably want to flatten your action first, as different constituents may have different preferences.

   for my $action ($work->flatten) {
     my $preference = $self->preference('code', 'command');
     push @serialized, ($preference eq 'code')
       ? [ eval => $action->to_code ] 
       : [ exec => $action->to_command ];
   }
      

Primitives

On primitive actions, all serialization methods will return a single item list. There are two types of of primitive actions shipped with this dist: Command and Code. Commands are essentially an abstraction around a call to an external command, Codes are an abstraction around a piece of Perl code. While these are all implementing the same interfaces, they have their own (hopefully obvious) preferences on how to be treated. "flatten" is just an identity operator for primitive actions.

Composites

Composite actions are actions that may consist out of multiple actions (though in some cases they may contain only one or even zero actions). "flatten" will return all its constituents. "execute", "to_code" and "to_command" will all call their respective method on all those values. "preference" is of little use, and will always prefer to flatten when given that option.

Nodes

Nodes are composite Actions. Nodes are a simple class with three attributes:

• target

  This is the filename of the result of this build step.

• dependencies

  This is an unordered set of zero or more files that must be build (and must be up-to-date) before the target is build.

• actions

  This is a sequence of zero or more actions that must be performed to build the target.

Essentially, a Node is equivalent to entry in a Makefile

Plans

Plans are the equivalent of a (piece of a) Makefile. They are a bunch of nodes that should interconnect. It has one attribute.

•

nodes

This is a hash mapping (target) names to nodes.

The "run" method will perform a topological sort much like "make". It will check which steps are necessary and skip the ones which are not.

Makefile.PL

 use ExtUtils::MakeMaker;
 use ExtUtils::Builder::MakeMaker;
 ...
 WriteMakeFile(
   NAME => 'Foo',
   VERSION => 0.001,
   ...,
 );
 sub MY::make_plans {
   my ($self, $planner) = @_;
   Frobnicator->add_plans($planner);
 }