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