NAME

src/mmd.c - Multimethod dispatch for binary opcode functions

SYNOPSIS

This system is set up to handle type-based dispatching for binary (i.e. two-arg) functions. This includes, though isn't necessarily limited to, binary operators such as addition or subtraction.

DESCRIPTION

The MMD system is straightforward, and currently must be explicitly invoked, for example by a vtable function. (We may reserve the right to use MMD in all circumstances, but currently do not).

API

For the purposes of the API, each MMD-able function is assigned a unique number which is used to find the correct function table. This is the func_num parameter in the following functions. While Parrot isn't restricted to a predefined set of functions, it does set things up so that all the binary vtable functions have a MMD table preinstalled for them, with default behaviour.

Remarks

binop_mmd_funcs->x and ->y are table sizes not highest type in table.

Functions

mmd_deref

If value is a reference-like PMC, dereference it so we can make an MMD call on the 'real' value.

mmd_ensure_writable

Make sure pmc is writable enough for function.

mmd_dispatch_p_ppp

Dispatch to a multimethod that returns a PMC. left, right, and dest are all PMC pointers, while func_num is the MMD table that should be used to do the dispatching. If the dest pointer is NULL, it dispatches two a two-argument function that returns a new dest always.

The MMD system will figure out which function should be called based on the types of left and right and call it, passing in left, right, and possibly dest like any other binary vtable function.

mmd_dispatch_p_pip

Like above, right argument is a native INTVAL.

mmd_dispatch_p_pnp

Like above, right argument is a native FLOATVAL.

mmd_dispatch_p_psp

Like above, right argument is a native STRING *.

mmd_dispatch_v_pp

mmd_dispatch_v_pi

mmd_dispatch_v_pn

mmd_dispatch_v_ps

Inplace dispatch functions for left <op=> right.

mmd_dispatch_i_pp

Like mmd_dispatch_p_ppp(), only it returns an INTVAL. This is used by MMD compare functions.

mmd_add_function

Add a new binary MMD function to the list of functions the MMD system knows of. func_num is the number of the new function. function is ignored.

RT#45941 change this to a MMD register interface that takes a function *name*.

mmd_expand_x

Expands the function table in the X dimension to include new_x.

mmd_expand_y

Expands the function table in the Y direction.

mmd_add_by_class

Add a function to the MMD table by class name, rather than class number. Handles the case where the named class isn't loaded yet.

Adds a new MMD function funcptr to the func_num function table that will be invoked when the left parameter is of class left_class and the right parameter is of class right_class. Both classes are STRING *s that hold the PMC class names for the left and right sides. If either class isn't yet loaded, Parrot will cache the information such that the function will be installed if at some point in the future both classes are available.

Currently this is done by just assigning class numbers to the classes, which the classes will pick up and use if they're later loaded, but we may later put the functions into a deferred table that we scan when PMC classes are loaded. Either way, the function will be guaranteed to be installed when it's needed.

The function table must exist, but if it is too small, it will automatically be expanded.

mmd_register

Register a function funcptr for MMD function table func_num for classes left_type and right_type. The left and right types are INTVALs that represent the class ID numbers.

The function table must exist, but if it is too small, it will automatically be expanded.

Adding a new function to the table can be interestingly non-trivial, so we get to be tricky.

If the left or right types are larger than anything we've seen so far, it means that we have to expand the table. Making Y larger is simple -- just realloc with some more rows. Making X larger is less simple. In either case, we punt to other functions.

RT#45943 - Currently the MMD system doesn't handle inheritance and best match searching, as it assumes that all PMC types have no parent type. This can be considered a bug, and will be resolved at some point in the future.

mmd_destroy

Frees all the memory allocated used the MMD subsystem.

mmd_vtfind

Return an MMD PMC function for the given data types. The return result is either a Sub PMC (for PASM MMD functions) or a NCI PMC holding the C function pointer in PMC_struct_val.

Parrot_mmd_sort_candidate_list

Given an array PMC (usually a MultiSub) sort the mmd candidates by their manhatten distance to the current args.

mmd_arg_tuple_inline

Return a list of argument types. PMC arguments are specified as function arguments.

mmd_arg_tuple_func

Return a list of argument types. PMC arguments are take from registers according to calling conventions.

mmd_search_default

Default implementation of MMD search. Search scopes for candidates, walk the class hierarchy, sort all candidates by their Manhattan distance, and return result

mmd_search_classes

Search all the classes in all MultiSubs of the candidates cl and return a list of all candidates. start_at_parent is 0 to start at the class itself or 1 to search from the first parent class.

mmd_sort_candidates

Sort the candidate list cl by Manhattan Distance

mmd_search_scopes

Search all scopes for MMD candidates matching the arguments given in arg_tuple.

mmd_is_hidden

Check if the given multi sub is hidden by any inner multi sub (already in the candidate list cl.

mmd_maybe_candidate

If the candidate pmc is a Sub PMC, push it on the candidate list and return TRUE to stop further search.

If the candidate is a MultiSub remember all matching Subs and return FALSE to continue searching outer scopes.

mmd_search_cur_namespace

Search the current package namespace for matching candidates. Return TRUE if the MMD search should stop.

mmd_search_builtin

Search the builtin namespace for matching candidates. This is the last search in all the namespaces.

Parrot_mmd_register_table

Register MMD functions for this PMC type.

Parrot_mmd_rebuild_table

Rebuild the static MMD_table for the given class type and MMD function number. If type is negative all classes are rebuilt. If func_nr is negative all MMD functions are rebuilt.

SEE ALSO

include/parrot/mmd.h, http://svn.perl.org/perl6/doc/trunk/design/apo/A12.pod, http://svn.perl.org/perl6/doc/trunk/design/syn/S12.pod