Added src/macro_helpers.h that supports application of preprocessor-macros

pull/275/head
Florian Fleissner 7 years ago
parent 2257402a43
commit 3119b6b228

@ -0,0 +1,103 @@
#pragma once
// Code generated by muli-line pre-processor macros is hard to read after
// pre-processing.
//
// When you want to check pre-processed code, e.g. for debugging or
// to understand what's going on, do the following:
//
// 1) Add the compiler command line definition
// -DKALEIDOSCOPE_ENABLE_MACRO_NEWLINE_SUBSTITUTION
// This prevents the __NL__ macro being defined below.
// 2) Generate the preprocessed code (it will contain a lot of __NL__ definitions).
// 3) Open the pre-processed code in your favorite editor.
// 3.1) Replace all __NL__ with newline characters.
// In vim the command would be ':%s/__NL__/\r/g'.
// 3.2) Autocorrect code-indenting to improve readability. This is necessary
// as pre-processor macros remove all whitespaces at the beginning of lines.
// With vim, the command gg=G helps (just type the characters one after
// the other).
// 4) Don't forget to remove the
// -DKALEIDOSCOPE_ENABLE_MACRO_NEWLINE_SUBSTITUTION
// from your compiler command line. Else the code won't compile.
#ifndef KALEIDOSCOPE_ENABLE_MACRO_NEWLINE_SUBSTITUTION
#define __NL__
#endif
#define __NN__
// Allow for the creation of verbose messages in static_asserts
//
#define VEROSE_STATIC_ASSERT_HEADER \
__NL__ "\n***************************************************************" \
__NL__ "\n******************** READ THIS CAREFULLY! *********************" \
__NL__ "\n***************************************************************" \
__NL__ "\n"
#define VERBOSE_STATIC_ASSERT_FOOTER \
__NL__ "\n" \
__NL__ "\n***************************************************************" \
__NL__ "\n***************************************************************" \
__NL__ "\n***************************************************************"
// The macro function RESTRICT_ARGS_COUNT can be used to generate more
// verbose error messages when users supply an insuitable number of arguments
// to a macro.
//
// For a macro it is used wherever one of the arguments A, B, C might
// be used, e.g.
//
#if 0 // This is just so that A_MACRO is not actually defined
#define A_MACRO(A, B, C, ...) \
(void)RESTRICT_ARGS_COUNT(0, 3, A_MACRO, ##__VA_ARGS__); \
int a = A; \
int b = B; \
int c = C;
#endif
//
// Note that RESTRICT_ARGS_COUNT can also be invoked wherever one of the macro
// arguments is used, e.g.
//
#if 0 // This is just so that B_MACRO is not actually defined
#define B_MACRO(A, B, C, ...)
int array[] = { A, B, RESTRICT_ARGS_COUNT(C, 3, B_MACRO, ##__VA_ARGS__) };
#endif
//
#define RESTRICT_ARGS_COUNT(B, \
NUM_EXPECTED_ARGS, \
ORIGINAL_MACRO, \
...) \
__NN__ ( \
__NL__ []{ /* Here we are in the body of a dummy lambda function. \
__NN__ []{} is, BTW, the shortest way to write a lambda. \
__NN__ It is only used to hold the static_assert that cannot be \
__NN__ defined directly in the keymap initializer list. By using the \
__NN__ comma operator ((A, B) always evaluates to b), we ensure \
__NN__ that not the lambda but B is what ASSERT_ARGS_COUNT \
__NN__ finally evaluates to. \
__NN__ Please not that passing B through this macro is a must \
__NN__ as we need it for the comma operator to work. \
__NN__ */ \
__NN__ static_assert(sizeof(const char) == sizeof(/*(const char*[]){*/ #__VA_ARGS__ /*}*/), \
__NN__ /* sizeof((int[]){ __VA_ARGS__ }) evaluates to \
__NN__ non-zero if __VA_ARGS__ is non-empty and zero otherwise. \
__NN__ */ \
__NN__ VEROSE_STATIC_ASSERT_HEADER \
__NN__ \
__NL__ "\nStrange arguments encountered in call to " #ORIGINAL_MACRO "." \
__NL__ "\n" \
__NL__ "\nPlease make sure to pass exactly " #NUM_EXPECTED_ARGS \
__NN__ " macro arguments to" \
__NL__ "\n" #ORIGINAL_MACRO ". Also make sure that there are no dangling" \
__NL__ "\ncommas at the end of the argument list. This is the superfluous" \
__NL__ "\npart at the end of the macro arguments list." \
__NL__ "\n" \
__NL__ "\n\'" #__VA_ARGS__ "\'" \
__NN__ \
__NN__ VERBOSE_STATIC_ASSERT_FOOTER \
__NL__ ); \
__NL__ }, /* End of dummy lambda, the comma operator's A operand. */ \
__NL__ B /* The overall ASSERT_ARGS_COUNT evaluates to B. */ \
__NL__ )
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