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Add some alternate forms for `const T a`

static_polymorphism
Bradlee Speice 2020-08-30 10:49:33 -04:00
parent 5e25faf5fd
commit b2f7575ef5
1 changed files with 40 additions and 2 deletions
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42
_posts/2020-08-05-static-polymorphism.md
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@ -219,8 +219,46 @@ int main() {
}
```
May be better off defining `const T` methods in one concept, `T` methods in another, and then having
one concept that `requires` the sub-concepts, but just trying to demonstrate what is possible.
Alternate alternate form:
```c++
template <typename T>
concept ConstMethod = requires {
requires requires (const T a) {
{ a.const_method() } -> std::same_as<std::uint64_t>;
};
requires requires (T a) {
{ a.nonconst_method() } -> std::same_as<std::uint64_t>;
{ a.unnecessary_const_method() } -> std::same_as<std::uint64_t>;
};
};
```
Third alternate form:
```c++
template<typename T>
concept ConstMethods = requires (const T a) {
{ a.const_method() } -> std::same_as<std::uint64_t>;
};
template<typename T>
concept NonConstMethods = requires (T a) {
{ a.nonconst_method() } -> std::same_as<std::uint64_t>;
{ a.unnecessary_const_method() } -> std::same_as<std::uint64_t>;
};
template <typename T>
concept ConstMethod = requires {
requires ConstMethods<T>;
requires NonConstMethods<T>;
};
```
...which goes a long way towards explaining why the "requires requires" form is necessary. Not sure
what the "best practices" form is, just trying to demonstrate what is possible.
Working with `const` parameters can be a bit weird because of implicit copies: