Daftar Isi

• NAME
• DESCRIPTION
• Callbacks
• Caching
• Examples
• AUTHORS

NAME

perlmroapi - Perl method resolution plugin interface

DESCRIPTION

As of Perl 5.10.1 there is a new interface for plugging and using methodresolution orders other than the default (linear depth first search).The C3 method resolution order added in 5.10.0 has been re-implemented asa plugin, without changing its Perl-space interface.

Each plugin should register itself by providingthe following structure

 struct mro_alg {
 
 AV *(*resolve)(pTHX_ HV *stash, U32 level);
 
 const char *name;
 
 U16 length;
 
 U16 kflags;
 
 U32 hash;
 
 };
 

and calling Perl_mro_register:

 Perl_mro_register(aTHX_ &my_mro_alg);
 

• resolve

  Pointer to the linearisation function, described below.

• name

  Name of the MRO, either in ISO-8859-1 or UTF-8.

• length

  Length of the name.

• kflags

  If the name is given in UTF-8, set this to HVhek_UTF8. The value is passeddirect as the parameter kflags to hv_common().

• hash

  A precomputed hash value for the MRO's name, or 0.

Callbacks

The resolve function is called to generate a linearised ISA for thegiven stash, using this MRO. It is called with a pointer to the stash, anda level of 0. The core always sets level to 0 when it calls yourfunction - the parameter is provided to allow your implementation to trackdepth if it needs to recurse.

The function should return a reference to an array containing the parentclasses in order. The names of the classes should be the result of callingHvENAME() on the stash. In those cases where HvENAME() returns null,HvNAME() should be used instead.

The caller is responsible for incrementing the reference count of the arrayreturned if it wants to keep the structure. Hence, if you have created atemporary value that you keep no pointer to, sv_2mortal() to ensure thatit is disposed of correctly. If you have cached your return value, thenreturn a pointer to it without changing the reference count.

Caching

Computing MROs can be expensive. The implementation provides a cache, inwhich you can store a single SV *, or anything that can be cast toSV *, such as AV *. To read your private value, use the macroMRO_GET_PRIVATE_DATA(), passing it the mro_meta structure from thestash, and a pointer to your mro_alg structure:

 meta = HvMROMETA(stash);
 
 private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg);
 

To set your private value, call Perl_mro_set_private_data():

 Perl_mro_set_private_data(aTHX_ meta, &c3_alg, private_sv);
 

The private data cache will take ownership of a reference to private_sv,much the same way that hv_store() takes ownership of a reference to thevalue that you pass it.

Examples

For examples of MRO implementations, see S_mro_get_linear_isa_c3()and the BOOT: section of mro/mro.xs, and S_mro_get_linear_isa_dfs()in mro.c

AUTHORS

The implementation of the C3 MRO and switchable MROs within the perl core waswritten by Brandon L Black. Nicholas Clark created the pluggable interface, refactored Brandon's implementation to work with it, and wrote this document.