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update doc

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Neargye 2020-01-25 22:55:18 +05:00
parent a576c077be
commit 06a8669d49
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doc/limitations.md
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@ -8,29 +8,48 @@
* Enum value must be in range `[MAGIC_ENUM_RANGE_MIN, MAGIC_ENUM_RANGE_MAX]`. By default `MAGIC_ENUM_RANGE_MIN = -128`, `MAGIC_ENUM_RANGE_MAX = 128`.
If need another range for all enum types by default, redefine the macro `MAGIC_ENUM_RANGE_MIN` and `MAGIC_ENUM_RANGE_MAX`.
```cpp
#define MAGIC_ENUM_RANGE_MIN 0
#define MAGIC_ENUM_RANGE_MAX 256
#include <magic_enum.hpp>
* `MAGIC_ENUM_RANGE_MAX` must be greater than `0` and must be less than `INT16_MAX`.
* `MAGIC_ENUM_RANGE_MIN` must be less or equals than `0` and must be greater than `INT16_MIN`.
* If need another range for all enum types by default, redefine the macro `MAGIC_ENUM_RANGE_MIN` and `MAGIC_ENUM_RANGE_MAX`.
```cpp
#define MAGIC_ENUM_RANGE_MIN 0
#define MAGIC_ENUM_RANGE_MAX 256
#include <magic_enum.hpp>
```
If need another range for specific enum type, add specialization `enum_range` for necessary enum type.
```cpp
#include <magic_enum.hpp>
enum number { one = 100, two = 200, three = 300 };
namespace magic_enum {
template <>
struct enum_range<number> {
static constexpr int min = 100; // Must be greater than `INT16_MIN`.
static constexpr int max = 300; // Must be less than `INT16_MAX`.
};
}
```
* If you hit a message like this:
```text
[...]
note: constexpr evaluation hit maximum step limit; possible infinite loop?
```
If need another range for specific enum type, add specialization `enum_range` for necessary enum type.
```cpp
#include <magic_enum.hpp>
enum number { one = 100, two = 200, three = 300 };
namespace magic_enum {
template <>
struct enum_range<number> {
static constexpr int min = 100;
static constexpr int max = 300;
};
}
```
Change the limit for the number of constexpr evaluated:
* MSVC `/constexpr:depthN`, `/constexpr:stepsN` <https://docs.microsoft.com/en-us/cpp/build/reference/constexpr-control-constexpr-evaluation>
* Clang `-fconstexpr-depth=N`, `-fconstexpr-steps=N` <https://clang.llvm.org/docs/UsersManual.html#controlling-implementation-limits>
* 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>
* `magic_enum` obtains the first defined value enums, and won't work if value are aliased.
```cpp
enum ShapeKind {
ConvexBegin = 0,
@ -44,7 +63,9 @@
// magic_enum::enum_cast<ShapeKind>("Box") -> std::nullopt
// magic_enum::enum_name(ShapeKind::Box) -> "ConvexBegin"
```
Work around the issue:
```cpp
enum ShapeKind {
// Convex shapes, see ConvexBegin and ConvexEnd below.