Recommend #pragma once for self-iteration
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Compilers implement the "multiple-include optimization" for included files when they can detect that subsequent includes will have no effect. With Clang, GCC, and Microsoft Visual Studio this will occur when encountering a `#pragma once`, or when there is a **top-level** include guard. The idiom of self-inclusion with Boost Preprocessor requires that the include guard is nested within the `#if !BOOST_PP_IS_ITERATING` and therefore does not meet the strict criteria for the previously mentioned build optimization. The documentation has been updated to suggest `#pragma once` after all self-includes have occurred. This will allow the compiler to avoid any subsequent includes for the current translation unit and avoid extra work for the preprocessor.
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Compilers implement the "multiple-include optimization" for included files when they can detect that subsequent includes will have no effect. With Clang, GCC, and Microsoft Visual Studio this will occur when encountering a
#pragma once, or when there is a top-level include guard.The idiom of self-inclusion with Boost Preprocessor requires that the include guard is nested within the
#if !BOOST_PP_IS_ITERATINGand therefore does not meet the strict criteria for the previously mentioned build optimization.The documentation has been updated to suggest
#pragma onceafter all self-includes have occurred. This will allow the compiler to avoid any subsequent includes for the current translation unit and avoid extra work for the preprocessor.