| // Copyright 2020 The Pigweed Authors |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| // use this file except in compliance with the License. You may obtain a copy of |
| // the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| // License for the specific language governing permissions and limitations under |
| // the License. |
| |
| // Macros for working with arguments to function-like macros. |
| #pragma once |
| |
| #include "pw_preprocessor/boolean.h" |
| #include "pw_preprocessor/internal/arg_count_impl.h" |
| |
| // Expands to a comma followed by __VA_ARGS__, if __VA_ARGS__ is non-empty. |
| // Otherwise, expands to nothing. If the final argument is empty, it is omitted. |
| // This is useful when passing __VA_ARGS__ to a variadic function or template |
| // parameter list, since it removes the extra comma when no arguments are |
| // provided. PW_COMMA_ARGS must NOT be used when invoking a macro from another |
| // macro. |
| // |
| // This is a more flexible, standard-compliant version of ##__VA_ARGS__. Unlike |
| // ##__VA_ARGS__, this can be used to eliminate an unwanted comma when |
| // __VA_ARGS__ expands to an empty argument because an outer macro was called |
| // with __VA_ARGS__ instead of ##__VA_ARGS__. Also, since PW_COMMA_ARGS drops |
| // the last argument if it is empty, both MY_MACRO(1, 2) and MY_MACRO(1, 2, ) |
| // can work correctly. |
| // |
| // PW_COMMA_ARGS must NOT be used to conditionally include a comma when invoking |
| // a macro from another macro. PW_COMMA_ARGS only functions correctly when the |
| // macro expands to C or C++ code! Using it with intermediate macros can result |
| // in out-of-order parameters. When invoking one macro from another, simply pass |
| // __VA_ARGS__. Only the final macro that expands to C/C++ code should use |
| // PW_COMMA_ARGS. |
| // |
| // For example, the following does NOT work: |
| /* |
| #define MY_MACRO(fmt, ...) \ |
| NESTED_MACRO(fmt PW_COMMA_ARGS(__VA_ARGS__)) // BAD! Do not do this! |
| */ |
| // Instead, only use PW_COMMA_ARGS when the macro expands to C/C++ code: |
| /* |
| #define MY_MACRO(fmt, ...) \ |
| NESTED_MACRO(fmt, __VA_ARGS__) // Pass __VA_ARGS__ to nested macros |
| |
| #define NESTED_MACRO(fmt, ...) \ |
| printf(fmt PW_COMMA_ARGS(__VA_ARGS__)) // PW_COMMA_ARGS is OK here |
| */ |
| #define PW_COMMA_ARGS(...) \ |
| _PW_IF(PW_EMPTY_ARGS(__VA_ARGS__), _PW_EXPAND, _PW_COMMA_ARGS) \ |
| (PW_DROP_LAST_ARG_IF_EMPTY(__VA_ARGS__)) |
| |
| #define _PW_COMMA_ARGS(...) , __VA_ARGS__ |
| |
| // Allows calling a different function-like macros based on the number of |
| // arguments. For example: |
| // |
| // #define ARG_PRINT(...) PW_DELEGATE_BY_ARG_COUNT(_ARG_PRINT, __VA_ARGS__) |
| // #define _ARG_PRINT1(a) LOG_INFO("1 arg: %s", a) |
| // #define _ARG_PRINT2(a, b) LOG_INFO("2 args: %s, %s", a, b) |
| // #define _ARG_PRINT3(a, b, c) LOG_INFO("3 args: %s, %s, %s", a, b, c) |
| // |
| // This can the be called from C/C++ code: |
| // |
| // ARG_PRINT("a"); // Outputs: 1 arg: a |
| // ARG_PRINT("a", "b"); // Outputs: 2 args: a, b |
| // ARG_PRINT("a", "b", "c"); // Outputs: 3 args: a, b, c |
| // |
| #define PW_DELEGATE_BY_ARG_COUNT(function, ...) \ |
| _PW_DELEGATE_BY_ARG_COUNT( \ |
| _PW_PASTE2(function, PW_FUNCTION_ARG_COUNT(__VA_ARGS__)), \ |
| PW_DROP_LAST_ARG_IF_EMPTY(__VA_ARGS__)) |
| |
| #define _PW_DELEGATE_BY_ARG_COUNT(function, ...) function(__VA_ARGS__) |
| |
| // PW_MACRO_ARG_COUNT counts the number of arguments it was called with. It |
| // evalulates to an integer literal in the range 0 to 64. Counting more than 64 |
| // arguments is not currently supported. |
| // |
| // PW_MACRO_ARG_COUNT is most commonly used to count __VA_ARGS__ in a variadic |
| // macro. For example, the following code counts the number of arguments passed |
| // to a logging macro: |
| // |
| /* #define LOG_INFO(format, ...) { \ |
| static const int kArgCount = PW_MACRO_ARG_COUNT(__VA_ARGS__); \ |
| SendLog(kArgCount, format, ##__VA_ARGS__); \ |
| } |
| */ |
| // clang-format off |
| #define PW_MACRO_ARG_COUNT(...) \ |
| _PW_MACRO_ARG_COUNT_IMPL(__VA_ARGS__, \ |
| 64, 63, 62, 61, 60, 59, 58, 57, \ |
| 56, 55, 54, 53, 52, 51, 50, 49, \ |
| 48, 47, 46, 45, 44, 43, 42, 41, \ |
| 40, 39, 38, 37, 36, 35, 34, 33, \ |
| 32, 31, 30, 29, 28, 27, 26, 25, \ |
| 24, 23, 22, 21, 20, 19, 18, 17, \ |
| 16, 15, 14, 13, 12, 11, 10, 9, \ |
| 8, 7, 6, 5, 4, 3, 2, PW_HAS_ARGS(__VA_ARGS__)) |
| // clang-format on |
| |
| // Argument count for using with a C/C++ function or template parameter list. |
| // The difference from PW_MACRO_ARG_COUNT is that the last argument is not |
| // counted if it is empty. This makes it easier to drop the final comma when |
| // expanding to C/C++ code. |
| #define PW_FUNCTION_ARG_COUNT(...) \ |
| _PW_FUNCTION_ARG_COUNT(PW_LAST_ARG(__VA_ARGS__), __VA_ARGS__) |
| |
| #define _PW_FUNCTION_ARG_COUNT(last_arg, ...) \ |
| _PW_PASTE2(_PW_FUNCTION_ARG_COUNT_, PW_EMPTY_ARGS(last_arg))(__VA_ARGS__) |
| |
| #define _PW_FUNCTION_ARG_COUNT_0 PW_MACRO_ARG_COUNT |
| #define _PW_FUNCTION_ARG_COUNT_1(...) \ |
| PW_MACRO_ARG_COUNT(PW_DROP_LAST_ARG(__VA_ARGS__)) |
| |
| // Evaluates to the last argument in the provided arguments. |
| #define PW_LAST_ARG(...) \ |
| _PW_PASTE2(_PW_LAST_ARG_, PW_MACRO_ARG_COUNT(__VA_ARGS__))(__VA_ARGS__) |
| |
| // Evaluates to the provided arguments, excluding the final argument. |
| #define PW_DROP_LAST_ARG(...) \ |
| _PW_PASTE2(_PW_DROP_LAST_ARG_, PW_MACRO_ARG_COUNT(__VA_ARGS__))(__VA_ARGS__) |
| |
| // Evaluates to the arguments, excluding the final argument if it is empty. |
| #define PW_DROP_LAST_ARG_IF_EMPTY(...) \ |
| _PW_IF( \ |
| PW_EMPTY_ARGS(PW_LAST_ARG(__VA_ARGS__)), PW_DROP_LAST_ARG, _PW_EXPAND) \ |
| (__VA_ARGS__) |
| |
| // Expands to 1 if one or more arguments are provided, 0 otherwise. |
| #define PW_HAS_ARGS(...) PW_NOT(PW_EMPTY_ARGS(__VA_ARGS__)) |
| |
| // Expands to 0 if one or more arguments are provided, 1 otherwise. This |
| // approach is from Jens Gustedt's blog: |
| // https://gustedt.wordpress.com/2010/06/08/detect-empty-macro-arguments/ |
| // |
| // Normally, with a standard-compliant C preprocessor, it's impossible to tell |
| // whether a variadic macro was called with no arguments or with one argument. |
| // A macro invoked with no arguments is actually passed one empty argument. |
| // |
| // This macro works by checking for the presence of a comma in four situations. |
| // These situations give the following information about __VA_ARGS__: |
| // |
| // 1. It is two or more variadic arguments. |
| // 2. It expands to one argument surrounded by parentheses. |
| // 3. It is a function-like macro that produces a comma when invoked. |
| // 4. It does not interfere with calling a macro when placed between it and |
| // parentheses. |
| // |
| // If a comma is not present in 1, 2, 3, but is present in 4, then __VA_ARGS__ |
| // is empty. For this case (0001), and only this case, a corresponding macro |
| // that expands to a comma is defined. The presence of this comma determines |
| // whether any arguments were passed in. |
| // |
| // C++20 introduces __VA_OPT__, which would greatly simplify this macro. |
| #define PW_EMPTY_ARGS(...) \ |
| _PW_HAS_NO_ARGS(_PW_HAS_COMMA(__VA_ARGS__), \ |
| _PW_HAS_COMMA(_PW_MAKE_COMMA_IF_CALLED __VA_ARGS__), \ |
| _PW_HAS_COMMA(__VA_ARGS__()), \ |
| _PW_HAS_COMMA(_PW_MAKE_COMMA_IF_CALLED __VA_ARGS__())) |
| |
| // clang-format off |
| |
| #define _PW_HAS_COMMA(...) \ |
| _PW_MACRO_ARG_COUNT_IMPL(__VA_ARGS__, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \ |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0) |
| |
| #define _PW_MACRO_ARG_COUNT_IMPL(a64, a63, a62, a61, a60, a59, a58, a57, \ |
| a56, a55, a54, a53, a52, a51, a50, a49, \ |
| a48, a47, a46, a45, a44, a43, a42, a41, \ |
| a40, a39, a38, a37, a36, a35, a34, a33, \ |
| a32, a31, a30, a29, a28, a27, a26, a25, \ |
| a24, a23, a22, a21, a20, a19, a18, a17, \ |
| a16, a15, a14, a13, a12, a11, a10, a09, \ |
| a08, a07, a06, a05, a04, a03, a02, a01, \ |
| count, ...) \ |
| count |
| |
| // clang-format on |
| |
| #define _PW_HAS_NO_ARGS(a1, a2, a3, a4) \ |
| _PW_HAS_COMMA(_PW_PASTE_RESULTS(a1, a2, a3, a4)) |
| #define _PW_PASTE_RESULTS(a1, a2, a3, a4) _PW_HAS_COMMA_CASE_##a1##a2##a3##a4 |
| #define _PW_HAS_COMMA_CASE_0001 , |
| #define _PW_MAKE_COMMA_IF_CALLED(...) , |
