我理解单参数函数的C11泛型,如下所示:(来自here)
#define acos(X) _Generic((X), \
long double complex: cacosl, \
double complex: cacos, \
float complex: cacosf, \
long double: acosl, \
float: acosf, \
default: acos \
)(X)
但是,对于具有两个参数的函数来说似乎很痛苦,你需要将调用嵌套到_Generic
,这真的很难看;摘录自同一博客:
#define pow(x, y) _Generic((x), \
long double complex: cpowl, \
double complex: _Generic((y), \
long double complex: cpowl, \
default: cpow), \
float complex: _Generic((y), \
long double complex: cpowl, \
double complex: cpow, \
default: cpowf), \
long double: _Generic((y), \
long double complex: cpowl, \
double complex: cpow, \
float complex: cpowf, \
default: powl), \
default: _Generic((y), \
long double complex: cpowl, \
double complex: cpow, \
float complex: cpowf, \
long double: powl, \
default: pow), \
float: _Generic((y), \
long double complex: cpowl, \
double complex: cpow, \
float complex: cpowf, \
long double: powl, \
float: powf, \
default: pow) \
)(x, y)
是否有办法为多参数函数提供更多人类可读的泛型,例如:
#define plop(a,b) _Generic((a,b), \
(int,long): plopii, \
(double,short int): plopdd)(a,b)
提前感谢您的回复。基本的想法是为_Generic
设置一个宏包装器。
答案 0 :(得分:14)
鉴于_Generic
的控制表达式未被评估,我建议应用一些算术运算来进行适当的类型组合,并打开结果。因此:
#define OP(x, y) _Generic((x) + (y), \
long double complex: LDC_OP(x, y), \
double complex: DC_OP(x, y), \
... )
当然这仅适用于某些情况,但您可以随时展开“折叠”类型无效的那些情况。 (例如,这将使用链接char *
示例来处理数组-N-of-char vs printnl
,然后如果组合类型为int
,则为可以返回并查看char
和short
。)
答案 1 :(得分:12)
由于C没有元组,让我们创建自己的元组:
typedef struct {int _;} T_double_double;
typedef struct {int _;} T_double_int;
typedef struct {int _;} T_int_double;
typedef struct {int _;} T_int_int;
typedef struct { T_double_double Double; T_double_int Int;} T_double;
typedef struct { T_int_double Double; T_int_int Int;} T_int;
#define typeof1(X) \
_Generic( (X), \
int: (T_int){{0}}, \
double: (T_double){{0}} )
#define typeof2(X, Y) \
_Generic( (Y), \
int: typeof1(X).Int, \
double: typeof1(X).Double )
这是客户端代码:
#include <stdio.h>
#include "generics.h"
#define typename(X, Y) \
_Generic( typeof2(X, Y), \
T_int_int: "int, int\n", \
T_int_double: "int, double\n", \
T_double_double: "double, double\n", \
T_double_int: "double, int\n", \
default: "Something else\n" )
int main() {
printf(typename(1, 2));
printf(typename(1, 2.0));
printf(typename(1.0, 2.0));
printf(typename(1.0, 2));
return 0;
}
它有效:
~/workspace$ clang -Wall -std=c11 temp.c
~/workspace$ ./a.out
int, int
int, double
double, double
double, int
是的,您仍然需要以指数大小编写代码。但至少你可以重复使用它。
答案 2 :(得分:5)
这里的版本只需要您手动编写线性数量的代码,所有这些代码都与手头的事物直接相关(没有手工定义类型的大树)。首先,用法示例:
#include <stdio.h>
// implementations of print
void print_ii(int a, int b) { printf("int, int\n"); }
void print_id(int a, double b) { printf("int, double\n"); }
void print_di(double a, int b) { printf("double, int\n"); }
void print_dd(double a, double b) { printf("double, double\n"); }
void print_iii(int a, int b, int c) { printf("int, int, int\n"); }
void print_default(void) { printf("unknown arguments\n"); }
// declare as overloaded
#define print(...) OVERLOAD(print, (__VA_ARGS__), \
(print_ii, (int, int)), \
(print_id, (int, double)), \
(print_di, (double, int)), \
(print_dd, (double, double)), \
(print_iii, (int, int, int)) \
)
#define OVERLOAD_ARG_TYPES (int, double)
#define OVERLOAD_FUNCTIONS (print)
#include "activate-overloads.h"
int main(void) {
print(44, 47); // prints "int, int"
print(4.4, 47); // prints "double, int"
print(1, 2, 3); // prints "int, int, int"
print(""); // prints "unknown arguments"
}
这可能是您将要获得的最轻的语法。
现在有缺点/限制:
OVERLOADED_ARG_TYPES
-O1
)您还必须定义一个不带参数的X_default
函数;不要将此添加到重载声明块。这用于非匹配(如果你想直接调用它,用任何不匹配的值调用重载,比如复合文字匿名结构或其他东西)。
此处activate-overloads.h
:
// activate-overloads.h
#include <order/interpreter.h>
#define ORDER_PP_DEF_8dispatch_overload ORDER_PP_FN( \
8fn(8N, 8V, \
8do( \
8print( 8cat(8(static inline int DISPATCH_OVER_), 8N) ((int ac, int av[]) { return ) ), \
8seq_for_each_with_idx( \
8fn(8I, 8T, \
8let( (8S, 8tuple_to_seq(8tuple_at_1(8T))), \
8print( 8lparen (ac==) 8to_lit(8seq_size(8S)) ), \
8seq_for_each_with_idx(8fn(8I, 8T, 8print( (&&av[) 8I (]==) 8cat(8(K_), 8T) )), 0, 8S), \
8print( 8rparen (?) 8I (:) ) \
)), \
1, 8V), \
8print( ( -1; }) ) \
) ))
#define TYPES_TO_ENUMS(TS) ORDER_PP ( \
8do( \
8seq_for_each(8fn(8T, 8print( 8T (:) 8cat(8(K_), 8T) (,) )), \
8tuple_to_seq(8(TS))), \
8print( (default: -1) ) \
) \
)
#define ENUMERATE_TYPES(TS) enum OVERLOAD_TYPEK { ORDER_PP ( \
8seq_for_each(8fn(8V, 8print( 8V (,) )), 8types_to_vals(8tuple_to_seq(8(TS)))) \
) };
#define ORDER_PP_DEF_8types_to_vals ORDER_PP_FN( \
8fn(8S, 8seq_map(8fn(8T, 8cat(8(K_), 8T)), 8S)) )
ENUMERATE_TYPES(OVERLOAD_ARG_TYPES)
#define OVER_ARG_TYPE(V) _Generic((V), TYPES_TO_ENUMS(OVERLOAD_ARG_TYPES) )
#define OVERLOAD
ORDER_PP (
8seq_for_each(
8fn(8F,
8lets( (8D, 8expand(8adjoin( 8F, 8(()) )))
(8O, 8seq_drop(2, 8tuple_to_seq(8D))),
8dispatch_overload(8F, 8O) )),
8tuple_to_seq(8(OVERLOAD_FUNCTIONS))
)
)
#undef OVERLOAD
#define OVERLOAD(N, ARGS, ...) ORDER_PP ( \
8do( \
8print(8lparen), \
8seq_for_each_with_idx( \
8fn(8I, 8T, \
8lets( (8S, 8tuple_to_seq(8tuple_at_1(8T))) \
(8R, 8tuple_to_seq(8(ARGS))) \
(8N, 8tuple_at_0(8T)), \
8if(8equal(8seq_size(8S), 8seq_size(8R)), \
8do( \
8print( 8lparen (DISPATCH_OVER_##N) 8lparen 8to_lit(8seq_size(8R)) (,(int[]){) ), \
8seq_for_each(8fn(8A, 8print( (OVER_ARG_TYPE) 8lparen 8A 8rparen (,) )), 8R), \
8print( (-1}) 8rparen (==) 8I 8rparen (?) 8N 8lparen ), \
8let( (8P, 8fn(8A, 8T, \
8print( (_Generic) 8lparen 8lparen 8A 8rparen (,) 8T (:) 8A (,default:*) 8lparen 8T (*) 8rparen (0) 8rparen ) \
)), \
8ap(8P, 8seq_head(8R), 8seq_head(8S)), \
8seq_pair_with(8fn(8A, 8T, 8do(8print((,)), 8ap(8P, 8A, 8T))), 8seq_tail(8R), 8seq_tail(8S)) \
), \
8print( 8rparen (:) ) \
), \
8print(( )) ) \
)), \
1, 8tuple_to_seq(8((__VA_ARGS__))) \
), \
8print( 8cat(8(N), 8(_default)) (()) 8rparen) \
) \
)
这需要Vesa K的精彩Order preprocessor library。
它是如何工作的:OVERLOAD_ARG_TYPES
声明用于构建枚举,列出用作常量的所有参数类型。然后,可以通过在所有实现(右参数号)之间调度的大三元运算在调用者代码中替换对重载名称的每次调用。调度通过使用_Generic
从参数类型生成枚举值,将它们放在数组中,并使用自动生成的调度程序函数返回该类型组合的ID(原始块中的位置)来工作。如果ID匹配,则调用该函数。如果参数的类型错误,则会为未使用的实现调用生成虚拟值,以避免类型不匹配。
从技术上讲,这涉及到&#34;运行时&#34; dispatch,但由于每个类型ID都是常量且调度程序函数是static inline
,因此编译器应该很容易优化,除了有用的调用(并且GCC确实优化了它)。 / p>
这是之前发布的here技术的改进(同样的想法,现在使用漂亮和超轻的语法)。
答案 3 :(得分:3)
哦好吧...... 这是使用boost预处理器库(符合C99预处理器)的宏解决方案的开始。
我们的想法是提供一种通用语法,允许为任意数量的参数编写嵌套通用选择。为了保持“简单”,选择的表达式对于同一选择级别上的所有元素都是相同的(您可以定义另一种语法来单独更改每个级别选择上的控制表达式。)。
OP的这个例子
#define plop(a,b) _Generic((a,b), \
(int,long): plopii, \
(double,short int): plopdd)(a,b)
变为
#define plop(a,b) \
MULT_GENERIC((a,b), \
(int, (long, plopii)), \
(double, (short int, plopdd)) \
)(a,b)
虽然我猜一个人可以略微改变它,以获得类似的东西:
#define plop(a,b) \
MULT_GENERIC((a,b), \
(int, long: plopii), \
(double, short int: plopdd) \
)(a,b)
可以扩展三个参数:
#define plop(a,b,c) \
MULT_GENERIC((a,b,c), \
(int, (double, long: plopidl, int: plopidi)), \
(double, (short int, long: plopdsl)) \
)(a,b)
进一步评论:我认为OP的语法也可以完成,但它不够灵活,因为你必须为每个可能的第二个参数重复第一个参数,例如。
#define plop(a,b) _Generic((a,b), \
(int,long): plopii, \
(int,double): plobid \
(double,short int): plopdd)(a,b)
我的语法中的OP示例。请注意,您在这里获得的收益并不多,因为您仍需要特别指定每种类型,在这种情况下,第二种类型会针对不同的第一类型多次指定。
#define pow(x, y) MULT_GENERIC( \
(x, y), \
(long double complex, (default, cpowl) \
), \
(double complex, (long double complex, cpowl) \
, (default, cpow) \
), \
(float complex, (long double complex, cpowl) \
, (double complex, cpow) \
, (default, cpowf) \
), \
(long double, (long double complex, cpowl) \
, (double complex, cpow) \
, (float complex, cpowf) \
, (default, powl) \
), \
(default, (long double complex, cpowl) \
, (double complex, cpow) \
, (float complex, cpowf) \
, (long double, powl) \
, (default, pow) \
), \
(float, (long double complex, cpowl) \
, (double complex, cpow) \
, (float complex, cpowf) \
, (long double, powl) \
, (float, powf) \
, (default, pow) \
) \
) \
(x, y)
pow(x, y)
这解决了:
_Generic( (x), long double complex : _Generic( (y), default : cpowl ) , double complex : _Generic( (y), long double complex : cpowl , default : cpow ) , float complex : _Generic( (y), long double complex : cpowl , double complex : cpow , default : cpowf ) , long double : _Generic( (y), long double complex : cpowl , double complex : cpow , float complex : cpowf , default : powl ) , default : _Generic( (y), long double complex : cpowl , double complex : cpow , float complex : cpowf , long double : powl , default : pow ) , float : _Generic( (y), long double complex : cpowl , double complex : cpow , float complex : cpowf , long double : powl , float : powf , default : pow ) ) (x, y)
这是重新格式化的:
_Generic((x),
long double complex: _Generic((y), default: cpowl)
, double complex: _Generic((y),
long double complex: cpowl
, default: cpow)
, float complex: _Generic((y),
long double complex: cpowl
, double complex: cpow
, default: cpowf)
, long double: _Generic((y),
long double complex: cpowl
, double complex: cpow
, float complex: cpowf
, default: powl)
, default: _Generic((y),
long double complex: cpowl
, double complex: cpow
, float complex: cpowf
, long double: powl
, default: pow)
, float: _Generic((y)
, long double complex: cpowl
, double complex: cpow
, float complex: cpowf
, long double: powl
, float : powf
, default: pow)
)
(x, y)
由于递归性质,我不得不介绍宏的副本;这个解决方案还需要清理(我有点累)。宏:
#include <boost/preprocessor.hpp>
#define MULT_GENERIC_GET_ASSOC_SEQ(DATA_TUPLE) \
BOOST_PP_TUPLE_ELEM(2, DATA_TUPLE)
#define MULT_GENERIC_NTH_ASSOC_TUPLE(N, DATA_TUPLE) \
BOOST_PP_SEQ_ELEM( N, MULT_GENERIC_GET_ASSOC_SEQ(DATA_TUPLE) )
#define MULT_GENERIC_GET_TYPENAME(N, DATA_TUPLE) \
BOOST_PP_TUPLE_ELEM(0, MULT_GENERIC_NTH_ASSOC_TUPLE(N, DATA_TUPLE))
#define MULT_GENERIC_GET_EXPR( N, DATA_TUPLE ) \
BOOST_PP_TUPLE_ELEM(1, MULT_GENERIC_NTH_ASSOC_TUPLE(N, DATA_TUPLE))
#define MULT_GENERIC_LEVEL_REP1(z, N, DATA_TUPLE) \
MULT_GENERIC_GET_TYPENAME( N, DATA_TUPLE ) \
: \
BOOST_PP_TUPLE_ELEM(1, DATA_TUPLE) /*LEVEL_MACRO*/ ( \
BOOST_PP_TUPLE_ELEM(0, DATA_TUPLE) /*SEL_EXPR_SEQ*/ \
, BOOST_PP_SEQ_POP_FRONT( BOOST_PP_TUPLE_TO_SEQ(MULT_GENERIC_NTH_ASSOC_TUPLE(N, DATA_TUPLE)) ) \
)
#define MULT_GENERIC_LEVEL1(SEL_EXPR_SEQ, LEVEL_MACRO, ASSOC_SEQ) \
_Generic( \
(BOOST_PP_SEQ_HEAD(SEL_EXPR_SEQ)), \
BOOST_PP_ENUM( BOOST_PP_SEQ_SIZE(ASSOC_SEQ), MULT_GENERIC_LEVEL_REP1, (BOOST_PP_SEQ_POP_FRONT(SEL_EXPR_SEQ), LEVEL_MACRO, ASSOC_SEQ) ) \
)
#define MULT_GENERIC_LEVEL_REP2(z, N, DATA_TUPLE) \
MULT_GENERIC_GET_TYPENAME( N, DATA_TUPLE ) \
: \
BOOST_PP_TUPLE_ELEM(1, DATA_TUPLE) /*LEVEL_MACRO*/ ( \
BOOST_PP_TUPLE_ELEM(0, DATA_TUPLE) /*SEL_EXPR_SEQ*/ \
, BOOST_PP_SEQ_POP_FRONT( BOOST_PP_TUPLE_TO_SEQ(MULT_GENERIC_NTH_ASSOC_TUPLE(N, DATA_TUPLE)) ) \
)
#define MULT_GENERIC_LEVEL2(SEL_EXPR_SEQ, LEVEL_MACRO, ASSOC_SEQ) \
_Generic( \
(BOOST_PP_SEQ_HEAD(SEL_EXPR_SEQ)), \
BOOST_PP_ENUM( BOOST_PP_SEQ_SIZE(ASSOC_SEQ), MULT_GENERIC_LEVEL_REP2, (BOOST_PP_SEQ_POP_FRONT(SEL_EXPR_SEQ), LEVEL_MACRO, ASSOC_SEQ) ) \
)
#define MULT_GENERIC0(SEL_EXPR_SEQ, ASSOC_SEQ) \
BOOST_PP_SEQ_HEAD(ASSOC_SEQ)
#define MULT_GENERIC1(SEL_EXPR_SEQ, ASSOC_SEQ) \
MULT_GENERIC_LEVEL1( SEL_EXPR_SEQ, MULT_GENERIC0, ASSOC_SEQ )
#define MULT_GENERIC2(SEL_EXPR_SEQ, ASSOC_SEQ) \
MULT_GENERIC_LEVEL2( SEL_EXPR_SEQ, MULT_GENERIC1, ASSOC_SEQ )
#define MULT_GENERIC(SEL_EXPR_TUPLE, ...) \
BOOST_PP_CAT(MULT_GENERIC, BOOST_PP_TUPLE_SIZE(SEL_EXPR_TUPLE)) ( BOOST_PP_TUPLE_TO_SEQ(SEL_EXPR_TUPLE), BOOST_PP_TUPLE_TO_SEQ((__VA_ARGS__)) )
答案 4 :(得分:1)
我真的觉得上述解决方案并不比OP的原始实现更容易或更清晰。我认为最好的方法是保持简单,只需要用更多的宏来抽象宏。以下是一个例子。
#include<stdio.h>
double multiply_id ( int a, double b )
{
return a * b;
}
double multiply_di ( double a, int b )
{
return a * b;
}
double multiply_dd ( double a, double b )
{
return a * b;
}
int multiply_ii ( int a, int b )
{
return a * b;
}
/*
#define multiply(a,b) _Generic((a), \
int: _Generic((b), \
int: multiply_ii, \
double: multiply_id), \
double: _Generic((b), \
int: multiply_di, \
double: multiply_dd) ) (a,b)
*/
#define _G2(ParamB,ParamA_Type, TypeB1, TypeB1_Func, TypeB2, TypeB2_Func) \
ParamA_Type: _Generic((ParamB), \
TypeB1: TypeB1_Func, \
TypeB2: TypeB2_Func)
#define multiply(a,b) _Generic((a), \
_G2(b,int,int,multiply_ii,double,multiply_id), \
_G2(b,double,int,multiply_di,double,multiply_dd) ) (a,b)
int main(int argc, const char * argv[]) {
int i;
double d;
i = 5;
d = 5.5;
d = multiply( multiply(d, multiply(d,i) ) ,multiply(i,i) );
printf("%f\n", d);
return 0;
}
_G2
是两个参数泛型的宏。这可以很容易地扩展到_G3
或更多。诀窍是正常做,然后从它的形式构建一个宏。