NAME

Signature -- Interface definition for various signature classes

USAGE

  use Signature;                # Really!  That's all.

DESCRIPTION

Makepp is quite flexible in the algorithm it usese for deciding whether a target is out of date with respect to its dependencies. Most of this flexibility is due to various different implementations of the Signature class.

Each rule can have a different signature class associated with it, if necessary. In the makefile, the signature class is specified by using the :signature modifier, like this:

   %.o : %.c
           : signature special_build
           $(CC) $(CFLAGS) -c $(FIRST_DEPENDENCY) -o $(TARGET)

This causes the signature class Signature::special_build to be used for this particular rule.

Only one object from each different signature class is actually created; the object has no data, and its only purpose is to contain a blessed reference to the package that actually implements the functions. Each rule contains a reference to the Signature object that is appropriate for it. The object is found by the name of the Signature class. For example, the above rule uses the object referenced by $Signature::special_build::special_build. (The purpose of this naming scheme is to make it impossible to inherit accidently a singleton object, which would cause the wrong Signature class to be used.)

signature

   $signature = $sigobj->signature($objinfo);

This function returns a signature for the given object (usually a FileInfo class, but possibly some other kind of object). A signature is simply an ASCII string that will change if the object is modified.

$sigobj is the dummy Signature class object.

$objinfo is the a reference to makepp's internal description of that object and how it is to be built. See "Extending makepp" in makepp for details.

The default signature function simply calls $objinfo->signature, i.e., it uses the default signature function for objects of that class.

build_check

  $rebuild_code = $sigobj->build_check($target,
                                       $command_string,
                                       $cwd,
                                       $sorted_dependencies,
                                       $depndency_signatures);

Returns undef if the given target does not need rebuilding. May return any true value (at the moment) if the object needs rebuilding.

$target is the target we are trying to build. The function will probably have to look at the build information for the target (using $target->build_info_string) to find out how the target was built last time.

$command_string is the shell command(s) that will be executed if the file needs rebuilding.

$cwd is the default directory relative to the parent directory of the object that contained the file.

$sorted_dependencies is a string that contains the relative filenames of all dependencies, sorted in alphabetical order, and separated by "\01" characters. (Yes, I know it's a weird format, but it's much faster for comparison for the Signature class which is used most of the time.) If you need to split this apart into filenames, just use @sorted_dependencies = split(/\01/, $sorted_dependencies);

$dependency_signatures is a string that contains the signature for each one of those dependencies, int the same order, and separated by "\01" characters. Again, if you want to split into an array to make this more convenient to use, do @dependency_signatures = split(/\01/, $dependency_signatures);

check_move_or_link_target

 $substitute_target = $rule->check_move_or_link_target($target_info,
                                                       $command_string,
                                                       $cwd,
                                                       $sorted_dependencies,
                                                       $dependency_signatures);

This function is alled when the target doesn't exist or is out of date. We check to make sure there aren't other versions of the target around somewhere in a repository or variant build cache which are not out of date. If such an object is found, then we return that object's information.

Arguments are the same as to build_check().