Commit 34741cc4 authored by Craig Citro's avatar Craig Citro

Fix trac #506 -- error with overloading, pops up in cpp_classes

parent 4b26e417
......@@ -2227,49 +2227,78 @@ def is_promotion(src_type, dst_type):
def best_match(args, functions, pos=None):
"""
Finds the best function to be called
Error if no function fits the call or an ambiguity is find (two or more possible functions)
Given a list args of arguments and a list of functions, choose one
to call which seems to be the "best" fit for this list of arguments.
This function is used, e.g., when deciding which overloaded method
to dispatch for C++ classes.
We first eliminate functions based on arity, and if only one
function has the correct arity, we return it. Otherwise, we weight
functions based on how much work must be done to convert the
arguments, with the following priorities:
* identical types or pointers to identical types
* promotions
* non-Python types
That is, we prefer functions where no arguments need converted,
and failing that, functions where only promotions are required, and
so on.
If no function is deemed a good fit, or if two or more functions have
the same weight, we return None (as there is no best match). If pos
is not None, we also generate an error.
"""
# TODO: args should be a list of types, not a list of Nodes.
actual_nargs = len(args)
possibilities = []
bad_types = 0
from_type = None
target_type = None
candidates = []
errors = []
for func in functions:
error_mesg = ""
func_type = func.type
if func_type.is_ptr:
func_type = func_type.base_type
# Check function type
if not func_type.is_cfunction:
if not func_type.is_error and pos is not None:
error(pos, "Calling non-function type '%s'" % func_type)
return None
error_mesg = "Calling non-function type '%s'" % func_type
errors.append((func, error_mesg))
continue
# Check no. of args
max_nargs = len(func_type.args)
min_nargs = max_nargs - func_type.optional_arg_count
if actual_nargs < min_nargs \
or (not func_type.has_varargs and actual_nargs > max_nargs):
if actual_nargs < min_nargs or \
(not func_type.has_varargs and actual_nargs > max_nargs):
if max_nargs == min_nargs and not func_type.has_varargs:
expectation = max_nargs
elif actual_nargs < min_nargs:
expectation = "at least %s" % min_nargs
else:
expectation = "at most %s" % max_nargs
error_str = "Call with wrong number of arguments (expected %s, got %s)" \
error_mesg = "Call with wrong number of arguments (expected %s, got %s)" \
% (expectation, actual_nargs)
errors.append((func, error_mesg))
continue
if len(functions) == 1:
candidates.append((func, func_type))
# Optimize the most common case of no overloading...
return func
if len(candidates) == 1:
return candidates[0]
elif len(candidates) == 0:
if len(errors) == 1 and pos is not None:
error(pos, errors[0][1])
return None
possibilities = []
bad_types = []
for func, func_type in candidates:
score = [0,0,0]
for i in range(min(len(args), len(func_type.args))):
src_type = args[i].type
dst_type = func_type.args[i].type
if dst_type.assignable_from(src_type):
if src_type == dst_type or (dst_type.is_reference and \
src_type == dst_type.base_type) or \
dst_type.same_as(src_type):
src_type == dst_type.base_type) \
or dst_type.same_as(src_type):
pass # score 0
elif is_promotion(src_type, dst_type):
score[2] += 1
......@@ -2278,13 +2307,13 @@ def best_match(args, functions, pos=None):
else:
score[0] += 1
else:
bad_types = func
from_type = src_type
target_type = dst_type
error_mesg = "Invalid conversion from '%s' to '%s'"%(src_type,
dst_type)
bad_types.append((func, error_mesg))
break
else:
possibilities.append((score, func)) # so we can sort it
if len(possibilities):
if possibilities:
possibilities.sort()
if len(possibilities) > 1 and possibilities[0][0] == possibilities[1][0]:
if pos is not None:
......@@ -2292,10 +2321,10 @@ def best_match(args, functions, pos=None):
return None
return possibilities[0][1]
if pos is not None:
if bad_types:
error(pos, "Invalid conversion from '%s' to '%s'" % (from_type, target_type))
if len(bad_types) == 1:
error(pos, bad_types[0][1])
else:
error(pos, error_str)
error(pos, "no suitable method found")
return None
......
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