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So many different ways to express the same thing.

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Bradlee Speice 2020-08-30 13:41:39 -04:00
parent b2f7575ef5
commit a939ceaba7
1 changed files with 23 additions and 5 deletions
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_posts/2020-08-05-static-polymorphism.md
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@ -223,6 +223,18 @@ Alternate alternate form:
```c++ ```c++
template <typename T> template <typename T>
concept ConstMethod =
requires (const T a) {
{ a.const_method() } -> std::same_as<std::uint64_t>;
} &&
requires (T a) {
{ a.nonconst_method() } -> std::same_as<std::uint64_t>;
{ a.unnecessary_const_method() } -> std::same_as<std::uint64_t>;
};
// Formulated inside a `requires` block:
/*
template <typename T>
concept ConstMethod = requires { concept ConstMethod = requires {
requires requires (const T a) { requires requires (const T a) {
{ a.const_method() } -> std::same_as<std::uint64_t>; { a.const_method() } -> std::same_as<std::uint64_t>;
@ -233,6 +245,7 @@ concept ConstMethod = requires {
{ a.unnecessary_const_method() } -> std::same_as<std::uint64_t>; { a.unnecessary_const_method() } -> std::same_as<std::uint64_t>;
}; };
}; };
*/
``` ```
Third alternate form: Third alternate form:
@ -240,21 +253,26 @@ Third alternate form:
```c++ ```c++
template<typename T> template<typename T>
concept ConstMethods = requires (const T a) { concept ConstMethods = requires (const T a) {
{ a.const_method() } -> std::same_as<std::uint64_t>; { a.const_method() } -> std::same_as<std::uint64_t>;
}; };
template<typename T> template<typename T>
concept NonConstMethods = requires (T a) { concept NonConstMethods = requires (T a) {
{ a.nonconst_method() } -> std::same_as<std::uint64_t>; { a.nonconst_method() } -> std::same_as<std::uint64_t>;
{ a.unnecessary_const_method() } -> std::same_as<std::uint64_t>; { a.unnecessary_const_method() } -> std::same_as<std::uint64_t>;
}; };
template<typename T>
concept ConstMethod = ConstMethods<T> && NonConstMethods<T>;
// Formulated inside a requires block:
/*
template <typename T> template <typename T>
concept ConstMethod = requires { concept ConstMethod = requires {
requires ConstMethods<T>; requires ConstMethods<T>;
requires NonConstMethods<T>; requires NonConstMethods<T>;
}; };
*/
``` ```
...which goes a long way towards explaining why the "requires requires" form is necessary. Not sure ...which goes a long way towards explaining why the "requires requires" form is necessary. Not sure