Match std::integral_constant by adding operator() and by marking operator T as noexcept. Other minor changes.
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January 6, 2025 23:54
Conversion between pointers to unrelated types `Source` and `Target`
can be done with two `static_cast`'s
("upcast" to pointer to cv-void followed by "downcast")
=> (IMO) it should be done with `static_cast`
(in order not to give the impression that `reinterpret_cast` really is needed):
`T *ptr_target = static_cast <T *> (static_cast <void *> (ptr_source));`
(Maybe that was the original intent of introducing `pdata`.)
…bject. If the compiler does not optimize away the `pdata` function-local `static` object, it ends up occupying space in the data section and it is going to need a corresponding relocation entry (just in case the module is not loaded at the desired address, as is the case with ASLR in Windows Vista and later and in modern versions of Linux). I admit that, for the current code, both MSVC and GCC manage to optimize away `pdata` even if it is `static`. But Boost should be an example of good coding which can be applied even to more complicated source code, e.g. to source code which calls `opaque_function (&pdata)` (in which case, if `pdata` is static, both MSVC and GCC do emit an extra relocation). And for other more complex cases, a function-local static-storage-duration object costs even more (as compared to a function-local automatic-storage-duration object given C++11 rules for "thread-safe" initialization of function-local `static`s. And I wish to re-iterate that, in my opinion, a good way to cast a pointer-to-one-type to a pointer-to-an-unrelated-type is not by `reinterpret_cast` (which by the way makes `pdata` not needed any more), but by using pointer to (possibly cv-qualified) `void` as an intermediary pointer type: ``` return static_cast <const Target *> (static_cast <const void *> (pointer_to_source)) ``` or: ``` const void *const intermediary (pointer_to_source); // Not `static` for the general case. return static_cast <const Target *> (intermediary); ``` Therefore, if the authors kindly agree, we can make this code an example for this style.
In the C++ Standard Library, `std::integral_constant` has its `operator T` marked as `noexcept`: https://timsong-cpp.github.io/cppwp/meta.help We hereby do the same for the Boost version.
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reinterpret_cast with static_cast.std::integral_constant by adding operator() and by marking operator T as noexcept. Other minor changes.
In the C++ Standard Library, `std::integral_constant` has `operator()`: https://timsong-cpp.github.io/cppwp/meta.help We hereby add `operator()` for the Boost version.
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Conversion between pointers of unrelated types
SourceandTargetcan be done withstatic_cast=> IMO should be done withstatic_cast(in order not to give the impression thatreinterpret_castreally is needed):T *ptr_target = static_cast <T *> (static_cast <void *> (ptr_source));IMO
reinterpret_castshould be used for pointer-to-integral and integral-to-pointer conversions (only).