fnovplan.txt

来自「开放源码的编译器open watcom 1.6.0版的源代码」· 文本 代码 · 共 268 行

Assumptions:
------------
- issues of scope, hiding and access control for user-defined conversions
	are handled elsewhere
	(p216,270,273-276)

- all array parameter declarations are converted to pointer type
	(p309)

- issues of scope and hidden functions for overload resolution are
	handled elsewhere; this code needs only to deal with the
	functions it is provided
	(p310)

- issues of overloaded member functions and their access rules and static
	qualifiers are resolved elsewhere
	(p309,312)

- issues of default arguments are handled elsewhere
	(p316)

- issues of matching member functions that require an implied argument which
	points to the object of the proper type are resolved elsewhere,
	compiler assumptions concerning the type of the implied argument
	are resolved elsewhere
	(p316-317)

- a temporary may be needed for a T& parameter, the rule about not using
	temporaries for non-const references is handled elsewhere
	(p318,323)

- in the issue of user-defined conversions in conjunction with standard
	conversions in overloading resolution,
	standard conversions applied to the input of the user-defined
	conversion will be ignored.
	standard conversions applied to the output of the user-defined
	conversion will be considered.
	(p317-318,326-327)

- PC type modifiers (FAR,FAR16,HUGE,BASED...) have no impact on overload
	resolution
	
Rules For Function Selection:
-----------------------------
"If one function provides a better than or equal match for every
argument and provides a strictly better match than all other functions
for at least one argument, then it is called; otherwise the call is an
error." (p313)

"For purposes of argument matching, a nonstatic member function is
considered to have an extra argument specifying the object for which it
is called.  ...  No temporaries will be introduced for this extra
argument and no user-defined conversions will be applied to achieve a
type match." (p316)

"For a given actual argument, no sequence of conversions will be
considered that contains more than one user-defined conversion or that
can be shortened by deleting one or more conversions into another
sequence that leads to the type of the corresponding formal argument of
any function in consideration." (p317)

Conversion Rules:
-----------------
- the best match conversion sequence must be the one considered (p317)

Equivalent Types:
-----------------
- T, T&
- T, const T, volatile T
- T[], T*	(assumed implicit in type parsing)
- typedef is a synonym, not a distinct type
- ... (ellipsis) match any type

Distinguishable Types:
----------------------
- T&, const T&, volatile T&
- T*, const T*, volatile T*
- each enum
- char, unsigned char, signed char
- arrays by magnitude of second and subsequent dimensions

Integral Types:
---------------
	char
	signed char
	unsigned char
	long char
	unsigned short int
	signed short int
	signed int
	unsigned int
	signed long int
	unsigned long int
	enum

Floating Types:
---------------
	float
	double
	long double

Trivial Conversions:
--------------------
	from:	to:
	T	T&
	T&	T
	T[]	T*		(assumed implicit in type parsing)
	T(args)	T(*)(args)
	T	const T
	T	volatile T
	T*	const T*
	T*	volatile T*

Integral Promotions:
--------------------
	from:			to:
4.1	char			int
	signed char		int
	wide char		unsigned int
	unsigned char		int
	signed short int 	int
	unsigned short int 	unsigned int
	int bit-field		int
	enum 			depends on base-type used
4.3	float			double
	double			long double
local INTEL extensions:
	NEAR *			FAR *


Standard Conversions:
---------------------
	from:		to:
4.2	base		signed base
	base		unsigned base
	signed base	base
	signed base	unsigned base
	unsigned base	base
	unsigned base	signed base
			- base is one of { char, short int, int, long int }
			  (long char does not have signed or unsigned)
4.4,4.5	floating	integral
	integral	floating
4.6	constant 0	T* (null pointer)
	non-const T*	void*
	non-volatile T*	void*
	(T*)()		void*
	B*		A* (if conversion is unambiguous and
			    A is accessible to B) (null goes to null) (p36)
4.7	B&		A& (if conversion is unambiguous and
			    A is accessible to B) (p38)
4.8	constant 0	M* (null pointer to member)
	MA*		MB* (if inverse pointer to object conversion can
			      be performed) (p39)

User-Defined Conversions:
-------------------------
- constructors take one argument and convert to resulting class type
- conversion functions must be member operator functions of class X
	that convert class X into the resulting type
- conversion functions cannot specify argument type or return type,
	hence, they cannot be overloaded
- user-defined conversions are selected based on the resulting type
- no preference is given to user-defined conversion by constructor
	or conversion function or vice versa
- only one user-defined conversion can be used in a conversion sequence

Ranking Scheme:
---------------
---> 0. Null
r00	- place holder, not used
---> 1. Exact
r10	- exactly identical
r11	- zero or more trivial conversions
r12	- those that do not do the following are better than those that do
		T* to const T*
		T* to volatile T*
		T& to const T&
		T& to volatile T&
---> 2. Promotions
	- not mentioned in 1
r20	- only integral promotion
		and trivial conversions
---> 3. Standard Conversions
	- not mentioned in 2
r30	- only standard conversions
		and trivial conversions
r31	- C is derived from B, which is derived from A, C* to B* is
	  	better than C* to A*
r31	- C is derived from B, which is derived from A, C& to B& is
	  	better than C& to A&
r31	- pointer to member resolution follows the same class hierarchy
	  	as pointer to object and reference to object
r32	- B is derived from A, B* to A* is better than
		B* to void*
		B* to const void*
---> 4. User-Defined Conversions
	- not mentioned in 3
r40	- only one user-defined conversion
		and standard conversions on input and output
		and trivial conversions on input and output
r60	- if there is more than one applicable user-defined conversion,
		it is ambiguous and the function is no longer a candidate
---> 5. Ellipsis Conversions
r50	- use of any ellipsis is worst
---> 6. No Match
r60	- if no conversion can be made the function is no longer a candidate
---> 7. Initialized Value
r70	- initialized, no conversion has been attempted

Ranking names appear as follows in code:
----------------------------------------
r00	OV_RANK_NULL
r10	OV_RANK_EXACT
r11	OV_RANK_SAME
r13	OV_RANK_TRIVIAL
r20	OV_RANK_PROMOTION
r30	OV_RANK_STD_CONV
r31	OV_RANK_STD_CONV_DERIV
r32	OV_RANK_STD_CONV_VOID
r40	OV_RANK_UD_CONV
r50	OV_RANK_ELLIPSIS
r60	OV_RANK_NO_MATCH
r70	OV_RANK_INVALID

General Comparision Rules:
--------------------------
- order of and number of trivial conversions is irrelevant (p318)
- when comparing, a shorter sequence of equal rank is better (p318)
- if a user-defined conversion is used, no account is taken of the number of
	standard conversions on the input to the user-defined conversion,
	however, standard conversions on the output of the user-defined
	conversion are considered

Algorithm for Computing Rank of Conversion from src to tgt:
-----------------------------------------------------------
===input:
TYPE src
TYPE tgt
OV_RANK *rank

===output:
BOOLEAN	true  => convertable
        false => nonconvertable

===working storage:
wsrc, wtgt are pointers to arg type compare structures:
{
reference		- is this a reference?
original type ptr	- the original provided
leading flags		- any flags
reference flags		- flags after reference
basic type ptr		- basic type (skipping reference)
imbedded flags		- flags after basic type
final type ptr		- anything on 'of' from basic type
}

if errorRank( wsrc, wtgt, rank ) return FALSE
if ellipsisRank( wsrc, wtgt, rank ) return TRUE
if exactRank( wsrc, wtgt, rank ) return TRUE
if trivialRank( wsrc, wtgt, rank ) return FALSE
    promotionRank( wsrc, wtgt, rank )
    if stdRank( wsrc, wtgt, rank ) return FALSE
    if stdDrvRank( wsrc, wtgt, rank ) return FALSE
    if stdVoidRank( wsrc, wtgt, rank ) return FALSE
    if usrDefRank( wsrc, wtgt, rank ) return FALSE
return TRUE