perlmroapi - Perl method resolution plugin interface
As of Perl 5.10.1 there is a new interface for plugging and using method resolution orders other than the default (linear depth first search). The C3 method resolution order added in 5.10.0 has been re-implemented as a plugin, without changing its Perl-space interface.
Each plugin should register itself by providing the following structure
struct mro_alg { AV *(*resolve)(pTHX_ HV *stash, U32 level); const char *name; U16 length; U16 kflags; U32 hash;};and callingPerl_mro_register:
Perl_mro_register(aTHX_ &my_mro_alg);Pointer to the linearisation function, described below.
Name of the MRO, either in ISO-8859-1 or UTF-8.
Length of the name.
If the name is given in UTF-8, set this toHVhek_UTF8. The value is passed direct as the parameterkflags tohv_common().
A precomputed hash value for the MRO's name, or 0.
Theresolve function is called to generate a linearised ISA for the given stash, using this MRO. It is called with a pointer to the stash, and alevel of 0. The core always setslevel to 0 when it calls your function - the parameter is provided to allow your implementation to track depth if it needs to recurse.
The function should return a reference to an array containing the parent classes in order. The names of the classes should be the result of callingHvENAME() on the stash. In those cases whereHvENAME() returns null,HvNAME() should be used instead.
The caller is responsible for incrementing the reference count of the array returned if it wants to keep the structure. Hence, if you have created a temporary value that you keep no pointer to,sv_2mortal() to ensure that it is disposed of correctly. If you have cached your return value, then return a pointer to it without changing the reference count.
Computing MROs can be expensive. The implementation provides a cache, in which you can store a singleSV *, or anything that can be cast toSV *, such asAV *. To read your private value, use the macroMRO_GET_PRIVATE_DATA(), passing it themro_meta structure from the stash, and a pointer to yourmro_alg structure:
meta = HvMROMETA(stash);private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg);To set your private value, callPerl_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 thathv_store() takes ownership of a reference to the value that you pass it.
For examples of MRO implementations, seeS_mro_get_linear_isa_c3() and theBOOT: section ofmro/mro.xs, andS_mro_get_linear_isa_dfs() inmro.c
The implementation of the C3 MRO and switchable MROs within the perl core was written by Brandon L Black. Nicholas Clark created the pluggable interface, refactored Brandon's implementation to work with it, and wrote this document.
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