How to use the b2.build.property_set.empty function in b2

# Expand properties specified on the command line into multiple property
    # sets consisting of all legal property combinations. Each expanded property
    # set will be used for a single build run. E.g. if multiple toolsets are
    # specified then requested targets will be built with each of them.
    # The expansion is being performed as late as possible so that the feature
    # validation is performed after all necessary modules (including project targets
    # on the command line) have been loaded.
    if properties:
        expanded = []
        for p in properties:
            expanded.extend(build_request.convert_command_line_element(p))

        expanded = build_request.expand_no_defaults(expanded)
    else:
        expanded = [property_set.empty()]

    # Now that we have a set of targets to build and a set of property sets to
    # build the targets with, we can start the main build process by using each
    # property set to generate virtual targets from all of our listed targets
    # and any of their dependants.
    for p in expanded:
        manager.set_command_line_free_features(property_set.create(p.free()))

        for t in targets:
            try:
                g = t.generate(p)
                if not isinstance(t, ProjectTarget):
                    results_of_main_targets.extend(g.targets())
                virtual_targets.extend(g.targets())
            except ExceptionWithUserContext, e:
                e.report()

get_manager().errors()("In 'install':  property specified with target that requires relinking.")
                else:
                    (r, targets) = generators.construct(self.project(), name, "INSTALLED_" + t,
                                                        new_ps, [i])
                    assert isinstance(r, property_set.PropertySet)
                    staged_targets.extend(targets)
                    
            else:
                staged_targets.append(copy_file(self.project(), ename, i, new_ps))

            if not staged_targets:
                get_manager().errors()("Unable to generate staged version of " + i)

            result.extend(get_manager().virtual_targets().register(t) for t in staged_targets)

        return (property_set.empty(), result)

self.module2attributes[module_name] = attributes

        python_standalone = False
        if location:
            attributes.set("source-location", [location], exact=1)
        elif not module_name in ["test-config", "site-config", "user-config", "project-config"]:
            # This is a standalone project with known location. Set source location
            # so that it can declare targets. This is intended so that you can put
            # a .jam file in your sources and use it via 'using'. Standard modules
            # (in 'tools' subdir) may not assume source dir is set.
            attributes.set("source-location", self.loaded_tool_module_path_[module_name], exact=1)
            python_standalone = True

        attributes.set("requirements", property_set.empty(), exact=True)
        attributes.set("usage-requirements", property_set.empty(), exact=True)
        attributes.set("default-build", property_set.empty(), exact=True)
        attributes.set("projects-to-build", [], exact=True)
        attributes.set("project-root", None, exact=True)
        attributes.set("build-dir", None, exact=True)

        self.project_rules_.init_project(module_name, python_standalone)

        jamroot = False

        parent_module = None;
        if module_name == "test-config":
            # No parent
            pass
        elif module_name == "site-config":
            parent_module = "test-config"
        elif module_name == "user-config":
            parent_module = "site-config"

# This is a standalone project with known location. Set source location
                # so that it can declare targets. This is intended so that you can put
                # a .jam file in your sources and use it via 'using'. Standard modules
                # (in 'tools' subdir) may not assume source dir is set.
                source_location = standalone_path
                if not source_location:
                    source_location = self.loaded_tool_module_path_.get(module_name)
                if not source_location:
                    self.manager.errors()('Standalone module path not found for "{}"'
                                          .format(module_name))
                attributes.set("source-location", [source_location], exact=1)
                python_standalone = True

            attributes.set("requirements", property_set.empty(), exact=True)
            attributes.set("usage-requirements", property_set.empty(), exact=True)
            attributes.set("default-build", property_set.empty(), exact=True)
            attributes.set("projects-to-build", [], exact=True)
            attributes.set("project-root", None, exact=True)
            attributes.set("build-dir", None, exact=True)

            self.project_rules_.init_project(module_name, python_standalone)

            if parent_module:
                self.inherit_attributes(module_name, parent_module)
                attributes.set("parent-module", parent_module, exact=1)

            if jamroot:
                attributes.set("project-root", location, exact=1)

            parent = None
            if parent_module:
                parent = self.target(parent_module)

get_manager().errors()("In 'install':  property specified with target that requires relinking.")
                else:
                    (r, targets) = generators.construct(self.project(), name, "INSTALLED_" + t,
                                                        new_ps, [i])
                    assert isinstance(r, property_set.PropertySet)
                    staged_targets.extend(targets)

            else:
                staged_targets.append(copy_file(self.project(), ename, i, new_ps))

            if not staged_targets:
                get_manager().errors()("Unable to generate staged version of " + i)

            result.extend(get_manager().virtual_targets().register(t) for t in staged_targets)

        return (property_set.empty(), result)

def __init__ (self, manager, sources, action_name, prop_set):
        assert(isinstance(prop_set, property_set.PropertySet))
        assert type(sources) == types.ListType
        self.sources_ = sources
        self.action_name_ = action_name
        if not prop_set:
            prop_set = property_set.empty()
        self.properties_ = prop_set
        if not all(isinstance(v, VirtualTarget) for v in prop_set.get('implicit-dependency')):
            import pdb
            pdb.set_trace()

        self.manager_ = manager
        self.engine_ = self.manager_.engine ()
        self.targets_ = []

        # Indicates whether this has been actualized or not.
        self.actualized_ = False

        self.dependency_only_sources_ = []
        self.actual_sources_ = []

# Expand properties specified on the command line into multiple property
    # sets consisting of all legal property combinations. Each expanded property
    # set will be used for a single build run. E.g. if multiple toolsets are
    # specified then requested targets will be built with each of them.
    # The expansion is being performed as late as possible so that the feature
    # validation is performed after all necessary modules (including project targets
    # on the command line) have been loaded.
    if properties:
        expanded = []
        for p in properties:
            expanded.extend(build_request.convert_command_line_element(p))

        expanded = build_request.expand_no_defaults(expanded)
    else:
        expanded = [property_set.empty()]

    # Now that we have a set of targets to build and a set of property sets to
    # build the targets with, we can start the main build process by using each
    # property set to generate virtual targets from all of our listed targets
    # and any of their dependants.
    for p in expanded:
        manager.set_command_line_free_features(property_set.create(p.free()))

        for t in targets:
            try:
                g = t.generate(p)
                if not isinstance(t, ProjectTarget):
                    results_of_main_targets.extend(g.targets())
                virtual_targets.extend(g.targets())
            except ExceptionWithUserContext, e:
                e.report()

elif not module_name in ["test-config", "site-config", "user-config", "project-config"]:
                # This is a standalone project with known location. Set source location
                # so that it can declare targets. This is intended so that you can put
                # a .jam file in your sources and use it via 'using'. Standard modules
                # (in 'tools' subdir) may not assume source dir is set.
                source_location = standalone_path
                if not source_location:
                    source_location = self.loaded_tool_module_path_.get(module_name)
                if not source_location:
                    self.manager.errors()('Standalone module path not found for "{}"'
                                          .format(module_name))
                attributes.set("source-location", [source_location], exact=1)
                python_standalone = True

            attributes.set("requirements", property_set.empty(), exact=True)
            attributes.set("usage-requirements", property_set.empty(), exact=True)
            attributes.set("default-build", property_set.empty(), exact=True)
            attributes.set("projects-to-build", [], exact=True)
            attributes.set("project-root", None, exact=True)
            attributes.set("build-dir", None, exact=True)

            self.project_rules_.init_project(module_name, python_standalone)

            if parent_module:
                self.inherit_attributes(module_name, parent_module)
                attributes.set("parent-module", parent_module, exact=1)

            if jamroot:
                attributes.set("project-root", location, exact=1)

            parent = None
            if parent_module:

def run (self, project, name, prop_set, sources):
       return (property_set.empty(), [])

"""Given the target name specified in constructor, returns the
        name which should be really used, by looking at the  properties.
        The tag properties come in two flavour:
          - value,
          - @rule-name
        In the first case, value is just added to name
        In the second case, the specified rule is called with specified name,
        target type and properties and should return the new name.
        If not  property is specified, or the rule specified by
         returns nothing, returns the result of calling
        virtual-target.add-suffix"""
        assert isinstance(specified_name, basestring)
        if self.action_:
            ps = self.action_.properties()
        else:
            ps = property_set.empty()

        # FIXME: I'm not sure how this is used, need to check with
        # Rene to figure out how to implement
        #~ We add ourselves to the properties so that any tag rule can get
        #~ more direct information about the target than just that available
        #~ through the properties. This is useful in implementing
        #~ name changes based on the sources of the target. For example to
        #~ make unique names of object files based on the source file.
        #~ --grafik
        #ps = property_set.create(ps.raw() + ["%s" % "XXXX"])
        #ps = [ property-set.create [ $(ps).raw ] $(__name__) ] ;

        tag = ps.get("")

        if tag: