119 lines
4.2 KiB
Markdown
119 lines
4.2 KiB
Markdown
# Limitations
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* This library uses a compiler-specific hack (based on `__PRETTY_FUNCTION__` / `__FUNCSIG__`).
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* To check is magic_enum supported compiler use macro `MAGIC_ENUM_SUPPORTED` or constexpr constant `magic_enum::is_magic_enum_supported`.</br>
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If magic_enum used on unsupported compiler, occurs the compilation error. To suppress error define macro `MAGIC_ENUM_NO_CHECK_SUPPORT`.
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* Enum can't reflect if the enum is a forward declaration.
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* For enum-flags add `is_flags` to specialization `enum_range` for necessary enum type. Specialization of `enum_range` must be injected in `namespace magic_enum::customize`.
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```cpp
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enum class Directions { Up = 1 << 1, Down = 1 << 2, Right = 1 << 3, Left = 1 << 4 };
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template <>
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struct magic_enum::customize::enum_range<Directions> {
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static constexpr bool is_flags = true;
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};
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```
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* Enum value must be in range `[MAGIC_ENUM_RANGE_MIN, MAGIC_ENUM_RANGE_MAX]`.
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* By default `MAGIC_ENUM_RANGE_MIN = -128`, `MAGIC_ENUM_RANGE_MAX = 128`.
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* `MAGIC_ENUM_RANGE = (MAGIC_ENUM_RANGE_MAX - MAGIC_ENUM_RANGE_MIN)` must be less than `UINT16_MAX`.
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* If need another range for all enum types by default, redefine the macro `MAGIC_ENUM_RANGE_MIN` and `MAGIC_ENUM_RANGE_MAX`.
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```cpp
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#define MAGIC_ENUM_RANGE_MIN 0
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#define MAGIC_ENUM_RANGE_MAX 256
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#include <magic_enum.hpp>
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```
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* If need another range for specific enum type, add specialization `enum_range` for necessary enum type. Specialization of `enum_range` must be injected in `namespace magic_enum::customize`.
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```cpp
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#include <magic_enum.hpp>
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enum class number { one = 100, two = 200, three = 300 };
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template <>
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struct magic_enum::customize::enum_range<number> {
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static constexpr int min = 100;
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static constexpr int max = 300;
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// (max - min) must be less than UINT16_MAX.
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};
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```
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* `magic_enum` [won't work if a value is aliased](https://github.com/Neargye/magic_enum/issues/68). Work with enum-aliases is compiler-implementation-defined.
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```cpp
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enum ShapeKind {
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ConvexBegin = 0,
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Box = 0, // Won't work.
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Sphere = 1,
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ConvexEnd = 2,
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Donut = 2, // Won't work too.
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Banana = 3,
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COUNT = 4
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};
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// magic_enum::enum_cast<ShapeKind>("Box") -> nullopt
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// magic_enum::enum_name(ShapeKind::Box) -> "ConvexBegin"
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```
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One of the possible workaround the issue:
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```cpp
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enum ShapeKind {
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// Convex shapes, see ConvexBegin and ConvexEnd below.
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Box = 0,
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Sphere = 1,
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// Non-convex shapes.
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Donut = 2,
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Banana = 3,
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COUNT = Banana + 1,
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// Non-reflected aliases.
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ConvexBegin = Box,
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ConvexEnd = Sphere + 1
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};
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// magic_enum::enum_cast<ShapeKind>("Box") -> ShapeKind::Box
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// magic_enum::enum_name(ShapeKind::Box) -> "Box"
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// Non-reflected aliases.
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// magic_enum::enum_cast<ShapeKind>("ConvexBegin") -> nullopt
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// magic_enum::enum_name(ShapeKind::ConvexBegin) -> "Box"
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```
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On some compiler enum-aliases not supported, [for example Visual Studio 2017](https://github.com/Neargye/magic_enum/issues/36), macro `MAGIC_ENUM_SUPPORTED_ALIASES` will be undefined.
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```cpp
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enum Number {
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one = 1,
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ONE = 1
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};
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// magic_enum::enum_cast<Number>("one") -> nullopt
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// magic_enum::enum_name(Number::one) -> ""
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// magic_enum::enum_cast<Number>("ONE") -> nullopt
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// magic_enum::enum_name(Number::ONE) -> ""
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```
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* If you hit a message like this:
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```text
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[...]
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note: constexpr evaluation hit maximum step limit; possible infinite loop?
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```
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Change the limit for the number of constexpr evaluated:
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* MSVC `/constexpr:depthN`, `/constexpr:stepsN` <https://docs.microsoft.com/en-us/cpp/build/reference/constexpr-control-constexpr-evaluation>
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* Clang `-fconstexpr-depth=N`, `-fconstexpr-steps=N` <https://clang.llvm.org/docs/UsersManual.html#controlling-implementation-limits>
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* GCC `-fconstexpr-depth=N`, `-fconstexpr-loop-limit=N`, `-fconstexpr-ops-limit=N` <https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/C_002b_002b-Dialect-Options.html>
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* Intellisense Visual Studio may have some problems analyzing `magic_enum`.
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* Enums in template may work incorrectly (especially on Сlang)
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See (#164)[https://github.com/Neargye/magic_enum/issues/164], (#65)[https://github.com/Neargye/magic_enum/issues/65]
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