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/*
* Copyright 2023 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef wasm_support_result_h
#define wasm_support_result_h
#include <string>
#include <variant>
namespace wasm {
// Represents a non-erroneous result with no associated data.
struct Ok {};
// Represents the non-erroneous absence of a result.
struct None {};
// Represents an erroneous result with associated error message.
struct Err {
std::string msg;
};
// Check a Result or MaybeResult for error and return the error if it exists.
#define CHECK_ERR(val) \
if (auto _val = (val); auto err = _val.getErr()) { \
return Err{*err}; \
}
// Represent a result of type T or an error message.
template<typename T = Ok> struct [[nodiscard]] Result {
std::variant<T, Err> val;
Result(Result<T>& other) = default;
Result(Result<T>&& other) = default;
Result(const Err& e) : val(std::in_place_type<Err>, e) {}
Result(Err&& e) : val(std::in_place_type<Err>, std::move(e)) {}
template<typename U = T>
Result(U&& u) : val(std::in_place_type<T>, std::forward<U>(u)) {}
Err* getErr() { return std::get_if<Err>(&val); }
T& operator*() { return *std::get_if<T>(&val); }
T* operator->() { return std::get_if<T>(&val); }
};
// Represent an optional result of type T or an error message.
template<typename T = Ok> struct [[nodiscard]] MaybeResult {
std::variant<T, None, Err> val;
MaybeResult() : val(None{}) {}
MaybeResult(MaybeResult<T>& other) = default;
MaybeResult(MaybeResult<T>&& other) = default;
MaybeResult(const Err& e) : val(std::in_place_type<Err>, e) {}
MaybeResult(Err&& e) : val(std::in_place_type<Err>, std::move(e)) {}
template<typename U = T>
MaybeResult(U&& u) : val(std::in_place_type<T>, std::forward<U>(u)) {}
template<typename U = T>
MaybeResult(Result<U>&& u)
: val(u.getErr() ? std::variant<T, None, Err>{*u.getErr()}
: std::variant<T, None, Err>{*u}) {}
// Whether we have an error or a value. Useful for assignment in loops and if
// conditions where errors should not get lost.
operator bool() const { return !std::holds_alternative<None>(val); }
MaybeResult<T>& operator=(const MaybeResult<T>&) = default;
MaybeResult<T>& operator=(MaybeResult<T>&&) = default;
Err* getErr() { return std::get_if<Err>(&val); }
T& operator*() { return *std::get_if<T>(&val); }
T* operator->() { return std::get_if<T>(&val); }
T* getPtr() { return std::get_if<T>(&val); }
};
} // namespace wasm
#endif // wasm_support_result_h
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