HTML::Mason::Component - Mason Component Class

- NAME
- SYNOPSIS
- DESCRIPTION
  - CREATING AND ACCESSING COMPONENTS
- METHODS
- FILE-BASED METHODS
- AUTHOR
- SEE ALSO

# NAME

HTML::Mason::Component - Mason Component Class

# SYNOPSIS

        my $comp1 = $m->current_comp;
        my $comp2 = $m->callers(1);
        my $comp3 = $m->fetch_comp('foo/bar');

        foreach ($comp1,$comp2,$comp3) {
           print "My name is ".$_->title.".\n";
        }

# DESCRIPTION

Mason uses the Component class to store components loaded into memory. Components come from three distinct sources:

1. File-based: loaded from a source or object file.

2. Subcomponents: embedded components defined with the `<%def>` tag.

3. Anonymous: created on-the-fly with the make_component Parser method.

Some of the methods below return different values (or nothing at all) depending on the component type.

The component API is primarily useful for introspection, e.g. ``what component called me'' or ``does the next component take a certain argument''. You can build complex Mason sites without ever dealing directly with a component object.

## CREATING AND ACCESSING COMPONENTS

Common ways to get handles on existing component objects include the current_comp, callers, and fetch_comp Request methods.

There is no published `new` method, because creating a component requires a parser. Use the make_component Parser method to create a new component dynamically.

Similarly, there is no `execute` or `call` method, because calling a component requires a request. All of the interfaces for calling a component (<& &>, `$m-`comp>, `$interp->exec` which normally take a component path, will also take a component object.

# METHODS

attr (name)
  Looks for the specified attribute in this component and its parents, returning the first value found. Dies with an error if not found. Attributes are declared in the `<%attr>` section.

attr_exists (name)
  Returns true if the specified attribute exists in this component or one of its parents, undef otherwise.

cache_file
  Returns the data cache filename for this component.

create_time
  Returns the time (in Perl `time()` format) when this component object was created.

declared_args
  Returns a reference to a hash of hashes representing the arguments declared in the `<%args>` section. The keys of the main hash are the variable names including prefix (e.g. `$foo`, `@lst`). Each secondary hash contains:

  - 'default': the string specified for default value (e.g. 'fido') or undef if none specified. Note that in general this is not the default value itself but rather an expression that gets evaluated every time the component runs.

  For example:

        # does $comp have an argument called $fido?
        if (exists($comp->declared_args->{'$fido'})) { ... }

        # does $fido have a default value?
        if (defined($comp->declared_args->{'$fido'}->{default})) { ... }

dir_path
  Returns the component's notion of a current directory, relative to the component root; this is used to resolve relative component paths. For file-based components this is the full component path minus the final piece. For subcomponents this is the same as its parent component. Undefined for anonymous components.

first_time
  Returns true if this is the first time the component has executed, false otherwise. Useful for initializing persistent component lexicals:

        if ($m->current_comp->first_time) {
           $dbh = DBI->connect(...);

  Note that in a web-based environment, this ``first time'' will come once for each child and every time the component is reloaded.

flag (name)
  Returns the value for the specified system flag. Flags are declared in the `<%flags>` section and affect the behavior of the component.

is_subcomp
  Returns true if this is a subcomponent of another component.

is_file_based
  Returns true if this component was loaded from a source or object file.

call_method (name, args...)
  Looks for the specified user-defined method in this component and its parents, calling the first one found. Dies with an error if not found. Methods are declared in the `<%method>` section.

method_exists (name)
  Returns true if the specified user-defined method exists in this component or one of its parents, undef otherwise.

name
  Returns a short name of the component. For file-based components this is the filename without the path. For subcomponents this is the name specified in `<%def>`. Undefined for anonymous components.

object_file
  Returns the object filename for this component.

owner
  Defined only for subcomponents; returns the component that this subcomponent was defined in.

parent
  Returns the parent of this component for inheritance purposes, by default the nearest `autohandler` in or above the component's directory. Can be changed via the `inherit` flag.

path
  Returns the absolute path of this component.

run_count
  Returns the number of times this component has been invoked. In a web-based environment, this value is separate for each child and resets every time the component is reloaded.

scall_method (name, args...)
  Like call_method (name, args...), but returns the method output as a string instead of printing it. (Think sprintf versus printf.) The method's return value is discarded.

subcomps
  With no arguments, returns a hashref containing the subcomponents defined in this component, with names as keys and component objects as values. With one argument, returns the subcomponent of that name or undef if no such subcomponent exists. e.g.

          if (my $subcomp = $comp->subcomps('.link')) {
              ...
          }

  Subcomponents are declared in the `<%def>` section.

title
  Returns a printable string denoting this component. It is intended to uniquely identify a component within a given interpreter although this is not 100% guaranteed. Mason uses this string in error messages, the previewer component trace, and `$m-`comp_stack>.

  For file-based components this is the component path. For subcomponents this is ``parent_component_path:subcomponent_name''. For anonymous components this is a unique label like ``[anon 17]''.

# FILE-BASED METHODS

The following methods apply only to file-based components (those loaded from source or object files). They return undef for other component types.

source_file
  Returns the source filename for this component.

source_dir
  Returns the directory of the source filename for this component.

# AUTHOR

Jonathan Swartz, swartz@pobox.com

# SEE ALSO

HTML::Mason::Request