Tasmota/lib/libesp32/Berry/default/static_block.hpp

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2021-05-21 22:04:42 +01:00
/**
* static_block.hpp
*
* An implementation of a Java-style static block, in C++ (and potentially a
* GCC/clang extension to avoid warnings). Almost, but not quite, valid C.
* Partially inspired by Andrei Alexandrescu's Scope Guard and
* discussions on stackoverflow.com
*
* By Eyal Rozenberg <eyalroz@technion.ac.il>
*
* Licensed under the Apache License v2.0:
* http://www.apache.org/licenses/LICENSE-2.0
*
*/
#pragma once
#ifndef STATIC_BLOCK_HPP_
#define STATIC_BLOCK_HPP_
#ifndef CONCATENATE
#define CONCATENATE(s1, s2) s1##s2
#define EXPAND_THEN_CONCATENATE(s1, s2) CONCATENATE(s1, s2)
#endif /* CONCATENATE */
#ifndef UNIQUE_IDENTIFIER
/**
* This macro expands into a different identifier in every expansion.
* Note that you _can_ clash with an invocation of UNIQUE_IDENTIFIER
* by manually using the same identifier elsewhere; or by carefully
* choosing another prefix etc.
*/
#ifdef __COUNTER__
#define UNIQUE_IDENTIFIER(prefix) EXPAND_THEN_CONCATENATE(prefix, __COUNTER__)
#else
#define UNIQUE_IDENTIFIER(prefix) EXPAND_THEN_CONCATENATE(prefix, __LINE__)
#endif /* COUNTER */
#else
#endif /* UNIQUE_IDENTIFIER */
/**
* Following is a mechanism for executing code statically.
*
* @note Caveats:
* - Your static block must be surround by curly braces.
* - No need for a semicolon after the block (but it won't hurt).
* - Do not put static blocks in files, as it might get compiled multiple
* times ane execute multiple times.
* - A static_block can only be used in file scope - not within any other block etc.
* - Templated static blocks will probably not work. Avoid them.
* - No other funny business, this is fragile.
* - This does not having any threading issues (AFAICT) - as it has no static
* initialization order issue. Of course, you have to _keep_ it safe with
* your static code.
* - Execution of the code is guaranteed to occur before main() executes,
* but the relative order of statics being initialized is unknown/unclear. So,
* do not call any method of an instance of a class which you expect to have been
* constructed; it may not have been. Instead, you can use a static getInstance() method
* (look this idiom up on the web, it's safe).
* - Variables defined within the static block are not global; they will
* go out of scope as soon as its execution concludes.
*
* Usage example:
*
* static_block {
* do_stuff();
* std::cout << "in the static block!\n";
* }
*
*/
#define static_block STATIC_BLOCK_IMPL1(UNIQUE_IDENTIFIER(_static_block_))
#define STATIC_BLOCK_IMPL1(prefix) \
STATIC_BLOCK_IMPL2(CONCATENATE(prefix,_fn),CONCATENATE(prefix,_var))
#define STATIC_BLOCK_IMPL2(function_name,var_name) \
static void function_name(); \
static int var_name __attribute((unused)) = (function_name(), 0) ; \
static void function_name()
#endif // STATIC_BLOCK_HPP_