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// Copyright 2022 The Pigweed Authors
//
// 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
//
// https://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.
//
// -----------------------------------------------------------------------------
// File: result.h
// -----------------------------------------------------------------------------
//
// An `Result<T>` represents a union of an `pw::Status` object and an object of
// type `T`. The `Result<T>` will either contain an object of type `T`
// (indicating a successful operation), or an error (of type `Status`)
// explaining why such a value is not present.
//
// In general, check the success of an operation returning an `Result<T>` like
// you would an `pw::Status` by using the `ok()` member function.
//
// Example:
//
// Result<Foo> result = Calculation();
// if (result.ok()) {
// result->DoSomethingCool();
// } else {
// PW_LOG_ERROR("Calculation failed: %s", result.status().str());
// }
#pragma once
#include <exception>
#include <functional>
#include <initializer_list>
#include <new>
#include <string>
#include <type_traits>
#include <utility>
#include "pw_preprocessor/compiler.h"
#include "pw_result/internal/result_internal.h"
#include "pw_status/status.h"
namespace pw {
// Returned Result objects may not be ignored.
template <typename T>
class [[nodiscard]] Result;
// Result<T>
//
// The `Result<T>` class template is a union of an `pw::Status` object and an
// object of type `T`. The `Result<T>` models an object that is either a usable
// object, or an error (of type `Status`) explaining why such an object is not
// present. An `Result<T>` is typically the return value of a function which may
// fail.
//
// An `Result<T>` can never hold an "OK" status; instead, the presence of an
// object of type `T` indicates success. Instead of checking for a `kOk` value,
// use the `Result<T>::ok()` member function. (It is for this reason, and code
// readability, that using the `ok()` function is preferred for `Status` as
// well.)
//
// Example:
//
// Result<Foo> result = DoBigCalculationThatCouldFail();
// if (result.ok()) {
// result->DoSomethingCool();
// } else {
// PW_LOG_ERROR("Calculation failed: %s", result.status().str());
// }
//
// Accessing the object held by an `Result<T>` should be performed via
// `operator*` or `operator->`, after a call to `ok()` confirms that the
// `Result<T>` holds an object of type `T`:
//
// Example:
//
// Result<int> i = GetCount();
// if (i.ok()) {
// updated_total += *i
// }
//
// NOTE: using `Result<T>::value()` when no valid value is present will trigger
// a PW_ASSERT.
//
// Example:
//
// Result<Foo> result = DoBigCalculationThatCouldFail();
// const Foo& foo = result.value(); // Crash/exception if no value present
// foo.DoSomethingCool();
//
// A `Result<T*>` can be constructed from a null pointer like any other pointer
// value, and the result will be that `ok()` returns `true` and `value()`
// returns `nullptr`. Checking the value of pointer in an `Result<T>` generally
// requires a bit more care, to ensure both that a value is present and that
// value is not null:
//
// Result<Foo*> result = LookUpTheFoo(arg);
// if (!result.ok()) {
// PW_LOG_ERROR("Unable to look up the Foo: %s", result.status().str());
// } else if (*result == nullptr) {
// PW_LOG_ERROR("Unexpected null pointer");
// } else {
// (*result)->DoSomethingCool();
// }
//
// Example factory implementation returning Result<T>:
//
// Result<Foo> FooFactory::MakeFoo(int arg) {
// if (arg <= 0) {
// return pw::Status::InvalidArgument();
// }
// return Foo(arg);
// }
template <typename T>
class Result : private internal_result::StatusOrData<T>,
private internal_result::CopyCtorBase<T>,
private internal_result::MoveCtorBase<T>,
private internal_result::CopyAssignBase<T>,
private internal_result::MoveAssignBase<T> {
template <typename U>
friend class Result;
using Base = internal_result::StatusOrData<T>;
public:
// Result<T>::value_type
//
// This instance data provides a generic `value_type` member for use within
// generic programming. This usage is analogous to that of
// `optional::value_type` in the case of `std::optional`.
typedef T value_type;
// Constructors
// Constructs a new `Result` with an `pw::Status::Unknown()` status. This
// constructor is marked 'explicit' to prevent usages in return values such as
// 'return {};', under the misconception that `Result<std::vector<int>>` will
// be initialized with an empty vector, instead of a `Status::Unknown()` error
// code.
explicit constexpr Result();
// `Result<T>` is copy constructible if `T` is copy constructible.
constexpr Result(const Result&) = default;
// `Result<T>` is copy assignable if `T` is copy constructible and copy
// assignable.
constexpr Result& operator=(const Result&) = default;
// `Result<T>` is move constructible if `T` is move constructible.
constexpr Result(Result&&) = default;
// `Result<T>` is moveAssignable if `T` is move constructible and move
// assignable.
constexpr Result& operator=(Result&&) = default;
// Converting Constructors
// Constructs a new `Result<T>` from an `pw::Result<U>`, when `T` is
// constructible from `U`. To avoid ambiguity, these constructors are disabled
// if `T` is also constructible from `Result<U>.`. This constructor is
// explicit if and only if the corresponding construction of `T` from `U` is
// explicit. (This constructor inherits its explicitness from the underlying
// constructor.)
template <
typename U,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<T, U>>,
std::is_constructible<T, const U&>,
std::is_convertible<const U&, T>,
std::negation<internal_result::
IsConstructibleOrConvertibleFromResult<T, U>>>::
value,
int> = 0>
constexpr Result(const Result<U>& other) // NOLINT
: Base(static_cast<const typename Result<U>::Base&>(other)) {}
template <
typename U,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<T, U>>,
std::is_constructible<T, const U&>,
std::negation<std::is_convertible<const U&, T>>,
std::negation<internal_result::
IsConstructibleOrConvertibleFromResult<T, U>>>::
value,
int> = 0>
explicit constexpr Result(const Result<U>& other)
: Base(static_cast<const typename Result<U>::Base&>(other)) {}
template <
typename U,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<T, U>>,
std::is_constructible<T, U&&>,
std::is_convertible<U&&, T>,
std::negation<internal_result::
IsConstructibleOrConvertibleFromResult<T, U>>>::
value,
int> = 0>
constexpr Result(Result<U>&& other) // NOLINT
: Base(static_cast<typename Result<U>::Base&&>(other)) {}
template <
typename U,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<T, U>>,
std::is_constructible<T, U&&>,
std::negation<std::is_convertible<U&&, T>>,
std::negation<internal_result::
IsConstructibleOrConvertibleFromResult<T, U>>>::
value,
int> = 0>
explicit constexpr Result(Result<U>&& other)
: Base(static_cast<typename Result<U>::Base&&>(other)) {}
// Converting Assignment Operators
// Creates an `Result<T>` through assignment from an
// `Result<U>` when:
//
// * Both `Result<T>` and `pw::Result<U>` are OK by assigning
// `U` to `T` directly.
// * `Result<T>` is OK and `pw::Result<U>` contains an error
// code by destroying `Result<T>`'s value and assigning from
// `Result<U>'
// * `Result<T>` contains an error code and `pw::Result<U>` is
// OK by directly initializing `T` from `U`.
// * Both `Result<T>` and `pw::Result<U>` contain an error
// code by assigning the `Status` in `Result<U>` to
// `Result<T>`
//
// These overloads only apply if `Result<T>` is constructible and
// assignable from `Result<U>` and `Result<T>` cannot be directly
// assigned from `Result<U>`.
template <typename U,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<T, U>>,
std::is_constructible<T, const U&>,
std::is_assignable<T, const U&>,
std::negation<
internal_result::
IsConstructibleOrConvertibleOrAssignableFromResult<
T,
U>>>::value,
int> = 0>
constexpr Result& operator=(const Result<U>& other) {
this->Assign(other);
return *this;
}
template <typename U,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<T, U>>,
std::is_constructible<T, U&&>,
std::is_assignable<T, U&&>,
std::negation<
internal_result::
IsConstructibleOrConvertibleOrAssignableFromResult<
T,
U>>>::value,
int> = 0>
constexpr Result& operator=(Result<U>&& other) {
this->Assign(std::move(other));
return *this;
}
// Constructs a new `Result<T>` with a non-ok status. After calling this
// constructor, `this->ok()` will be `false` and calls to `value()` will
// crash, or produce an exception if exceptions are enabled.
//
// The constructor also takes any type `U` that is convertible to `Status`.
// This constructor is explicit if an only if `U` is not of type `Status` and
// the conversion from `U` to `Status` is explicit.
//
// REQUIRES: !Status(std::forward<U>(v)).ok(). This requirement is DCHECKed.
// In optimized builds, passing OkStatus() here will have the effect of
// passing Status::Internal() as a fallback.
template <
typename U = Status,
std::enable_if_t<
std::conjunction<
std::is_convertible<U&&, Status>,
std::is_constructible<Status, U&&>,
std::negation<std::is_same<std::decay_t<U>, Result<T>>>,
std::negation<std::is_same<std::decay_t<U>, T>>,
std::negation<std::is_same<std::decay_t<U>, std::in_place_t>>,
std::negation<internal_result::
HasConversionOperatorToResult<T, U&&>>>::value,
int> = 0>
constexpr Result(U&& v) : Base(std::forward<U>(v)) {}
template <
typename U = Status,
std::enable_if_t<
std::conjunction<
std::negation<std::is_convertible<U&&, Status>>,
std::is_constructible<Status, U&&>,
std::negation<std::is_same<std::decay_t<U>, Result<T>>>,
std::negation<std::is_same<std::decay_t<U>, T>>,
std::negation<std::is_same<std::decay_t<U>, std::in_place_t>>,
std::negation<internal_result::
HasConversionOperatorToResult<T, U&&>>>::value,
int> = 0>
constexpr explicit Result(U&& v) : Base(std::forward<U>(v)) {}
template <
typename U = Status,
std::enable_if_t<
std::conjunction<
std::is_convertible<U&&, Status>,
std::is_constructible<Status, U&&>,
std::negation<std::is_same<std::decay_t<U>, Result<T>>>,
std::negation<std::is_same<std::decay_t<U>, T>>,
std::negation<std::is_same<std::decay_t<U>, std::in_place_t>>,
std::negation<internal_result::
HasConversionOperatorToResult<T, U&&>>>::value,
int> = 0>
constexpr Result& operator=(U&& v) {
this->AssignStatus(std::forward<U>(v));
return *this;
}
// Perfect-forwarding value assignment operator.
// If `*this` contains a `T` value before the call, the contained value is
// assigned from `std::forward<U>(v)`; Otherwise, it is directly-initialized
// from `std::forward<U>(v)`.
// This function does not participate in overload unless:
// 1. `std::is_constructible_v<T, U>` is true,
// 2. `std::is_assignable_v<T&, U>` is true.
// 3. `std::is_same_v<Result<T>, std::remove_cvref_t<U>>` is false.
// 4. Assigning `U` to `T` is not ambiguous:
// If `U` is `Result<V>` and `T` is constructible and assignable from
// both `Result<V>` and `V`, the assignment is considered bug-prone and
// ambiguous thus will fail to compile. For example:
// Result<bool> s1 = true; // s1.ok() && *s1 == true
// Result<bool> s2 = false; // s2.ok() && *s2 == false
// s1 = s2; // ambiguous, `s1 = *s2` or `s1 = bool(s2)`?
template <
typename U = T,
typename = typename std::enable_if<std::conjunction<
std::is_constructible<T, U&&>,
std::is_assignable<T&, U&&>,
std::disjunction<
std::is_same<std::remove_cv_t<std::remove_reference_t<U>>, T>,
std::conjunction<
std::negation<std::is_convertible<U&&, Status>>,
std::negation<
internal_result::HasConversionOperatorToResult<T, U&&>>>>,
internal_result::IsForwardingAssignmentValid<T, U&&>>::value>::type>
constexpr Result& operator=(U&& v) {
this->Assign(std::forward<U>(v));
return *this;
}
// Constructs the inner value `T` in-place using the provided args, using the
// `T(args...)` constructor.
template <typename... Args>
explicit constexpr Result(std::in_place_t, Args&&... args);
template <typename U, typename... Args>
explicit constexpr Result(std::in_place_t,
std::initializer_list<U> ilist,
Args&&... args);
// Constructs the inner value `T` in-place using the provided args, using the
// `T(U)` (direct-initialization) constructor. This constructor is only valid
// if `T` can be constructed from a `U`. Can accept move or copy constructors.
//
// This constructor is explicit if `U` is not convertible to `T`. To avoid
// ambiguity, this constructor is disabled if `U` is a `Result<J>`, where
// `J` is convertible to `T`.
template <
typename U = T,
std::enable_if_t<
std::conjunction<
internal_result::IsDirectInitializationValid<T, U&&>,
std::is_constructible<T, U&&>,
std::is_convertible<U&&, T>,
std::disjunction<
std::is_same<std::remove_cv_t<std::remove_reference_t<U>>, T>,
std::conjunction<
std::negation<std::is_convertible<U&&, Status>>,
std::negation<
internal_result::
HasConversionOperatorToResult<T, U&&>>>>>::value,
int> = 0>
constexpr Result(U&& u) // NOLINT
: Result(std::in_place, std::forward<U>(u)) {}
template <
typename U = T,
std::enable_if_t<
std::conjunction<
internal_result::IsDirectInitializationValid<T, U&&>,
std::disjunction<
std::is_same<std::remove_cv_t<std::remove_reference_t<U>>, T>,
std::conjunction<
std::negation<std::is_constructible<Status, U&&>>,
std::negation<
internal_result::
HasConversionOperatorToResult<T, U&&>>>>,
std::is_constructible<T, U&&>,
std::negation<std::is_convertible<U&&, T>>>::value,
int> = 0>
explicit constexpr Result(U&& u) // NOLINT
: Result(std::in_place, std::forward<U>(u)) {}
// Result<T>::ok()
//
// Returns whether or not this `Result<T>` holds a `T` value. This
// member function is analagous to `Status::ok()` and should be used
// similarly to check the status of return values.
//
// Example:
//
// Result<Foo> result = DoBigCalculationThatCouldFail();
// if (result.ok()) {
// // Handle result
// else {
// // Handle error
// }
[[nodiscard]] constexpr bool ok() const { return this->status_.ok(); }
// Result<T>::status()
//
// Returns a reference to the current `Status` contained within the
// `Result<T>`. If `pw::Result<T>` contains a `T`, then this function returns
// `OkStatus()`.
constexpr const Status& status() const&;
constexpr Status status() &&;
// Result<T>::value()
//
// Returns a reference to the held value if `this->ok()`. Otherwise,
// terminates the process.
//
// If you have already checked the status using `this->ok()`, you probably
// want to use `operator*()` or `operator->()` to access the value instead of
// `value`.
//
// Note: for value types that are cheap to copy, prefer simple code:
//
// T value = result.value();
//
// Otherwise, if the value type is expensive to copy, but can be left
// in the Result, simply assign to a reference:
//
// T& value = result.value(); // or `const T&`
//
// Otherwise, if the value type supports an efficient move, it can be
// used as follows:
//
// T value = std::move(result).value();
//
// The `std::move` on result instead of on the whole expression enables
// warnings about possible uses of the result object after the move.
constexpr const T& value() const& PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr T& value() & PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr const T&& value() const&& PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr T&& value() && PW_ATTRIBUTE_LIFETIME_BOUND;
// Result<T>:: operator*()
//
// Returns a reference to the current value.
//
// REQUIRES: `this->ok() == true`, otherwise the behavior is undefined.
//
// Use `this->ok()` to verify that there is a current value within the
// `Result<T>`. Alternatively, see the `value()` member function for a
// similar API that guarantees crashing or throwing an exception if there is
// no current value.
constexpr const T& operator*() const& PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr T& operator*() & PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr const T&& operator*() const&& PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr T&& operator*() && PW_ATTRIBUTE_LIFETIME_BOUND;
// Result<T>::operator->()
//
// Returns a pointer to the current value.
//
// REQUIRES: `this->ok() == true`, otherwise the behavior is undefined.
//
// Use `this->ok()` to verify that there is a current value.
constexpr const T* operator->() const PW_ATTRIBUTE_LIFETIME_BOUND;
constexpr T* operator->() PW_ATTRIBUTE_LIFETIME_BOUND;
// Result<T>::value_or()
//
// Returns the current value if `this->ok() == true`. Otherwise constructs a
// value using the provided `default_value`.
//
// Unlike `value`, this function returns by value, copying the current value
// if necessary. If the value type supports an efficient move, it can be used
// as follows:
//
// T value = std::move(result).value_or(def);
//
// Unlike with `value`, calling `std::move()` on the result of `value_or` will
// still trigger a copy.
template <typename U>
constexpr T value_or(U&& default_value) const&;
template <typename U>
constexpr T value_or(U&& default_value) &&;
// Result<T>::IgnoreError()
//
// Ignores any errors. This method does nothing except potentially suppress
// complaints from any tools that are checking that errors are not dropped on
// the floor.
constexpr void IgnoreError() const;
// Result<T>::emplace()
//
// Reconstructs the inner value T in-place using the provided args, using the
// T(args...) constructor. Returns reference to the reconstructed `T`.
template <typename... Args>
T& emplace(Args&&... args) {
if (ok()) {
this->Clear();
this->MakeValue(std::forward<Args>(args)...);
} else {
this->MakeValue(std::forward<Args>(args)...);
this->status_ = OkStatus();
}
return this->data_;
}
template <
typename U,
typename... Args,
std::enable_if_t<
std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value,
int> = 0>
T& emplace(std::initializer_list<U> ilist, Args&&... args) {
if (ok()) {
this->Clear();
this->MakeValue(ilist, std::forward<Args>(args)...);
} else {
this->MakeValue(ilist, std::forward<Args>(args)...);
this->status_ = OkStatus();
}
return this->data_;
}
// Result<T>::and_then()
//
// template <typename U>
// Result<U> and_then(Function<Result<U>(T)> func);
//
// Returns the Result from the invocation of the function on the contained
// value if it exists. Otherwise, returns the contained status in the Result.
//
// Result<Foo> CreateFoo();
// Result<Bar> CreateBarFromFoo(const Foo& foo);
//
// Result<Bar> bar = CreateFoo().and_then(CreateBarFromFoo);
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, T&>,
std::enable_if_t<std::is_copy_constructible_v<Ret>, int> = 0>
constexpr Ret and_then(Fn&& function) & {
static_assert(internal_result::IsResult<Ret>,
"Fn must return a pw::Result");
return ok() ? std::invoke(std::forward<Fn>(function), value())
: Ret(status());
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, T&&>,
std::enable_if_t<std::is_move_constructible_v<Ret>, int> = 0>
constexpr auto and_then(Fn&& function) && {
static_assert(internal_result::IsResult<Ret>,
"Fn must return a pw::Result");
return ok() ? std::invoke(std::forward<Fn>(function), std::move(value()))
: Ret(status());
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, const T&>,
std::enable_if_t<std::is_copy_constructible_v<Ret>, int> = 0>
constexpr auto and_then(Fn&& function) const& {
static_assert(internal_result::IsResult<Ret>,
"Fn must return a pw::Result");
return ok() ? std::invoke(std::forward<Fn>(function), value())
: Ret(status());
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, const T&&>,
std::enable_if_t<std::is_move_constructible_v<Ret>, int> = 0>
constexpr auto and_then(Fn&& function) const&& {
static_assert(internal_result::IsResult<Ret>,
"Fn must return a pw::Result");
return ok() ? std::invoke(std::forward<Fn>(function), std::move(value()))
: Ret(status());
}
// Result<T>::or_else()
//
// template <typename U>
// requires std::is_convertible_v<U, Result<T>>
// Result<T> or_else(Function<U(Status)> func);
//
// Result<T> or_else(Function<void(Status)> func);
//
// Returns a Result if it has a value, otherwise it invokes the given
// function. The function must return a type convertible to a Result<T> or a
// void.
//
// Result<Foo> CreateFoo();
//
// Result<Foo> foo = CreateFoo().or_else(
// [](Status s) { PW_LOG_ERROR("Status: %d", s.code()); });
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, const Status&>,
std::enable_if_t<!std::is_void_v<Ret>, int> = 0>
constexpr Result<T> or_else(Fn&& function) const& {
static_assert(std::is_convertible_v<Ret, Result<T>>,
"Fn must be convertible to a pw::Result");
return ok() ? *this : std::invoke(std::forward<Fn>(function), status());
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, const Status&>,
std::enable_if_t<std::is_void_v<Ret>, int> = 0>
constexpr Result<T> or_else(Fn&& function) const& {
if (ok()) {
return *this;
}
std::invoke(std::forward<Fn>(function), status());
return *this;
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, Status&&>,
std::enable_if_t<!std::is_void_v<Ret>, int> = 0>
constexpr Result<T> or_else(Fn&& function) && {
static_assert(std::is_convertible_v<Ret, Result<T>>,
"Fn must be convertible to a pw::Result");
return ok() ? std::move(*this)
: std::invoke(std::forward<Fn>(function), std::move(status()));
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, Status&&>,
std::enable_if_t<std::is_void_v<Ret>, int> = 0>
constexpr Result<T> or_else(Fn&& function) && {
if (ok()) {
return *this;
}
std::invoke(std::forward<Fn>(function), status());
return std::move(*this);
}
// Result<T>::transform()
//
// template <typename U>
// Result<U> transform(Function<U(T)> func);
//
// Returns a Result<U> which contains the result of the invocation of the
// given function if *this contains a value. Otherwise, it returns a Result<U>
// with the same Status as *this.
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, T&>,
std::enable_if_t<std::is_copy_constructible_v<Ret>, int> = 0>
constexpr Result<Ret> transform(Fn&& function) & {
if (!ok()) {
return status();
}
return std::invoke(std::forward<Fn>(function), value());
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, T&&>,
std::enable_if_t<std::is_move_constructible_v<Ret>, int> = 0>
constexpr Result<Ret> transform(Fn&& function) && {
if (!ok()) {
return std::move(status());
}
return std::invoke(std::forward<Fn>(function), std::move(value()));
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, T&>,
std::enable_if_t<std::is_copy_constructible_v<Ret>, int> = 0>
constexpr Result<Ret> transform(Fn&& function) const& {
if (!ok()) {
return status();
}
return std::invoke(std::forward<Fn>(function), value());
}
template <typename Fn,
typename Ret = internal_result::InvokeResultType<Fn, T&&>,
std::enable_if_t<std::is_move_constructible_v<Ret>, int> = 0>
constexpr Result<Ret> transform(Fn&& function) const&& {
if (!ok()) {
return std::move(status());
}
return std::invoke(std::forward<Fn>(function), std::move(value()));
}
private:
using Base::Assign;
template <typename U>
constexpr void Assign(const Result<U>& other);
template <typename U>
constexpr void Assign(Result<U>&& other);
};
// operator==()
//
// This operator checks the equality of two `Result<T>` objects.
template <typename T>
constexpr bool operator==(const Result<T>& lhs, const Result<T>& rhs) {
if (lhs.ok() && rhs.ok()) {
return *lhs == *rhs;
}
return lhs.status() == rhs.status();
}
// operator!=()
//
// This operator checks the inequality of two `Result<T>` objects.
template <typename T>
constexpr bool operator!=(const Result<T>& lhs, const Result<T>& rhs) {
return !(lhs == rhs);
}
//------------------------------------------------------------------------------
// Implementation details for Result<T>
//------------------------------------------------------------------------------
template <typename T>
constexpr Result<T>::Result() : Base(Status::Unknown()) {}
template <typename T>
template <typename U>
constexpr inline void Result<T>::Assign(const Result<U>& other) {
if (other.ok()) {
this->Assign(*other);
} else {
this->AssignStatus(other.status());
}
}
template <typename T>
template <typename U>
constexpr inline void Result<T>::Assign(Result<U>&& other) {
if (other.ok()) {
this->Assign(*std::move(other));
} else {
this->AssignStatus(std::move(other).status());
}
}
template <typename T>
template <typename... Args>
constexpr Result<T>::Result(std::in_place_t, Args&&... args)
: Base(std::in_place, std::forward<Args>(args)...) {}
template <typename T>
template <typename U, typename... Args>
constexpr Result<T>::Result(std::in_place_t,
std::initializer_list<U> ilist,
Args&&... args)
: Base(std::in_place, ilist, std::forward<Args>(args)...) {}
template <typename T>
constexpr const Status& Result<T>::status() const& {
return this->status_;
}
template <typename T>
constexpr Status Result<T>::status() && {
return ok() ? OkStatus() : std::move(this->status_);
}
template <typename T>
constexpr const T& Result<T>::value() const& {
PW_ASSERT(this->status_.ok());
return this->data_;
}
template <typename T>
constexpr T& Result<T>::value() & {
PW_ASSERT(this->status_.ok());
return this->data_;
}
template <typename T>
constexpr const T&& Result<T>::value() const&& {
PW_ASSERT(this->status_.ok());
return std::move(this->data_);
}
template <typename T>
constexpr T&& Result<T>::value() && {
PW_ASSERT(this->status_.ok());
return std::move(this->data_);
}
template <typename T>
constexpr const T& Result<T>::operator*() const& {
PW_ASSERT(this->status_.ok());
return this->data_;
}
template <typename T>
constexpr T& Result<T>::operator*() & {
PW_ASSERT(this->status_.ok());
return this->data_;
}
template <typename T>
constexpr const T&& Result<T>::operator*() const&& {
PW_ASSERT(this->status_.ok());
return std::move(this->data_);
}
template <typename T>
constexpr T&& Result<T>::operator*() && {
PW_ASSERT(this->status_.ok());
return std::move(this->data_);
}
template <typename T>
constexpr const T* Result<T>::operator->() const {
PW_ASSERT(this->status_.ok());
return &this->data_;
}
template <typename T>
constexpr T* Result<T>::operator->() {
PW_ASSERT(this->status_.ok());
return &this->data_;
}
template <typename T>
template <typename U>
constexpr T Result<T>::value_or(U&& default_value) const& {
if (ok()) {
return this->data_;
}
return std::forward<U>(default_value);
}
template <typename T>
template <typename U>
constexpr T Result<T>::value_or(U&& default_value) && {
if (ok()) {
return std::move(this->data_);
}
return std::forward<U>(default_value);
}
template <typename T>
constexpr void Result<T>::IgnoreError() const {
// no-op
}
namespace internal {
template <typename T>
constexpr Status ConvertToStatus(const Result<T>& result) {
return result.status();
}
template <typename T>
constexpr T ConvertToValue(Result<T>& result) {
return std::move(result.value());
}
} // namespace internal
} // namespace pw