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---
Language: Cpp
BasedOnStyle: WebKit
AllowAllParametersOfDeclarationOnNextLine: true
BinPackArguments: false
BinPackParameters: false
ColumnLimit: 100
ConstructorInitializerAllOnOneLineOrOnePerLine: true
Cpp11BracedListStyle: true
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
AlignAfterOpenBracket: true
AlwaysBreakAfterDefinitionReturnType: None
AlwaysBreakTemplateDeclarations: true
IndentCaseLabels: true
PenaltyReturnTypeOnItsOwnLine: 300
NamespaceIndentation: All
Standard: Cpp11

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.idea/

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cmake_minimum_required(VERSION 3.3)
project(maybe_result)
add_subdirectory(src)
add_subdirectory(tests)

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Copyright (c) 2016 TRAFI
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

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# Maybe Result
Maybe Result is a return value wrapper that can contain either a value
`T` or error `E`. It borrows ideas heavily from the [C++17's
`std::experimental::optional`][optional], [Rust's std::result](result) and
the [`std::expected`][expected] that was proposed but not yet accepted
for C++17.
[optional]: http://en.cppreference.com/w/cpp/experimental/optional
[result]: https://doc.rust-lang.org/std/result/
[expected]: https://github.com/ptal/expected
### How is it different from `std::experimental::optional`?
Has a value for error instead of `nullopt`.
### How is it different from `std::expected`?
It does not require the error to be an exception, and does not fall back to
exceptions. All values must be checked, similar to `std::experimental::optional`.
## Setting up
This is header-only library. We recommend to add `src` to included directories,
so that the include would be:
```cpp
#include <maybe/result.hpp>
```
A C++ compiler shat supports C++14 is required.
You can use `-std=c++14` flag for sufficiently recent versions of
`GCC` or `CLANG`.
__Warning! Library is highly experimental and is not guaranteed to work.__
## Running tests
```bash
cmake .
make tests && ./tests/tests
```
## License
Licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally
submitted for inclusion in the work by you, as defined in the Apache-2.0
license, shall be dual licensed as above, without any additional terms or
conditions.

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set(TARGET "maybe_result")
add_library(${TARGET} INTERFACE)
target_include_directories(${TARGET}
INTERFACE .
)

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/*
* Copyright 2016 TRAFI
*
* Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
* http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
* http://opensource.org/licenses/MIT>, at your option. This file may not be
* copied, modified, or distributed except according to those terms.
*
*/
#pragma once
namespace maybe {
template <typename T, typename E> class result;
}

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/*
* Copyright 2016 TRAFI
*
* Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
* http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
* http://opensource.org/licenses/MIT>, at your option. This file may not be
* copied, modified, or distributed except according to those terms.
*
*/
#pragma once
#include <stdexcept>
#include <string>
#include "result.fwd.hpp"
namespace maybe {
namespace internal {
enum class Value { OK, ERR, NONE };
struct Placeholder {
};
}
class bad_result_access : public std::logic_error {
public:
explicit bad_result_access(const std::string& what_arg) : logic_error{what_arg}
{
}
explicit bad_result_access(const char* what_arg) : logic_error{what_arg}
{
}
};
// workaround: std utility functions aren't constexpr yet
template <class T>
inline constexpr T&& constexpr_forward(typename std::remove_reference<T>::type& t) noexcept
{
return static_cast<T&&>(t);
}
template <class T>
inline constexpr T&& constexpr_forward(typename std::remove_reference<T>::type&& t) noexcept
{
static_assert(!std::is_lvalue_reference<T>::value, "!!");
return static_cast<T&&>(t);
}
template <typename T, typename E>
class result final {
public:
result() : tag(internal::Value::NONE)
{
}
/** ok initializer */
result(T&& value, internal::Placeholder) : tag(internal::Value::OK)
{
init_ok(std::forward<T>(value));
}
/** err initializer */
result(internal::Placeholder, E&& value) : tag(internal::Value::ERR)
{
init_err(std::forward<T>(value));
}
/** copy constructor */
result(const result& other) noexcept
{
copy_from(other);
}
/** copy assignment */
result& operator=(const result& other) noexcept
{
clear();
copy_from(other);
return *this;
}
/** move constructor */
result(result&& other) noexcept
{
set_from(other);
}
/** move assignment */
result& operator=(result&& other) noexcept
{
clear();
set_from(other);
return *this;
}
/** destructor */
~result<T, E>()
{
clear();
};
/** helper constructor for ok value */
constexpr static result<T, E> ok(T&& value) noexcept
{
return result<T, E>(std::forward<T>(value), internal::Placeholder{});
}
/** helper constructor for err value */
constexpr static result<T, E> err(E&& err) noexcept
{
return result<T, E>(internal::Placeholder{}, std::forward<E>(err));
}
constexpr bool is_ok() const noexcept
{
return tag == internal::Value::OK;
}
constexpr bool is_err() const noexcept
{
return tag == internal::Value::ERR;
}
constexpr T const& ok_value() const&
{
return is_ok() ? ok_val : (throw bad_result_access("bad ok result access"), ok_val);
}
constexpr T& ok_value() &
{
return is_ok() ? ok_val : (throw bad_result_access("bad ok result access"), ok_val);
}
constexpr E const& err_value() const&
{
return is_err() ? err_val
: (throw bad_result_access("bad err result access"), err_val);
}
constexpr E& err_value() &
{
return is_err() ? err_val
: (throw bad_result_access("bad err result access"), err_val);
}
template <class V>
constexpr T ok_value_or(V&& v) const&
{
return is_ok() ? ok_val : static_cast<T>(constexpr_forward<V>(v));
}
template <class V>
constexpr E err_value_or(V&& v) const&
{
return is_err() ? err_val : static_cast<E>(constexpr_forward<V>(v));
}
explicit constexpr operator bool() const noexcept
{
return is_ok();
}
constexpr T* ok_dataptr() const noexcept
{
return std::addressof(ok_val);
}
constexpr E* err_dataptr() const noexcept
{
return std::addressof(err_val);
}
private:
constexpr void copy_from(const result<T, E>& other) noexcept;
constexpr void set_from(result<T, E>& other) noexcept;
constexpr void init_ok(T&& value) noexcept;
constexpr void init_err(T&& value) noexcept;
constexpr void clear() noexcept;
internal::Value tag;
union {
T ok_val;
E err_val;
};
};
template <typename T, typename E>
constexpr bool operator==(const result<T, E>& x, const result<T, E>& y)
{
return x.is_ok() && y.is_ok()
? *x.ok_dataptr() == *y.ok_dataptr()
: (x.is_err() && y.is_err() ? *x.err_dataptr() == *y.err_dataptr() : false);
}
template <typename T, typename E>
constexpr bool operator!=(const result<T, E>& x, const result<T, E>& y)
{
return !(x == y);
}
}
#include "result.inline.hpp"

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/*
* Copyright 2016 TRAFI
*
* Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
* http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
* http://opensource.org/licenses/MIT>, at your option. This file may not be
* copied, modified, or distributed except according to those terms.
*
*/
#pragma once
#include "result.hpp"
template <typename T, typename E>
constexpr void maybe::result<T, E>::copy_from(const result<T, E>& other) noexcept
{
using maybe::internal::Value;
switch (other.tag) {
case Value::OK:
init_ok(*other.ok_dataptr());
break;
case Value::ERR:
init_err(*other.err_dataptr());
break;
default:
tag = Value::NONE;
break;
}
}
template <typename T, typename E>
constexpr void maybe::result<T, E>::set_from(result<T, E>& other) noexcept
{
using maybe::internal::Value;
switch (other.tag) {
case Value::OK:
init_ok(std::move(other.ok_val));
break;
case Value::ERR:
init_err(std::move(other.err_val));
break;
default:
tag = Value::NONE;
break;
}
other.tag = Value::NONE;
}
template <typename T, typename E>
constexpr void maybe::result<T, E>::init_ok(T&& value) noexcept
{
tag = maybe::internal::Value::OK;
::new (static_cast<void*>(ok_dataptr())) T(std::forward<T>(value));
}
template <typename T, typename E>
constexpr void maybe::result<T, E>::init_err(T&& value) noexcept
{
tag = maybe::internal::Value::ERR;
::new (static_cast<void*>(err_dataptr())) T(std::forward<T>(value));
}
template <typename T, typename E>
constexpr void maybe::result<T, E>::clear() noexcept
{
using maybe::internal::Value;
switch (tag) {
case Value::OK:
(&this->ok_val)->T::~T();
tag = Value::NONE;
break;
case internal::Value::ERR:
(&this->err_val)->E::~E();
tag = Value::NONE;
break;
default:
break;
}
}

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set(TARGET "tests")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
add_executable(${TARGET}
main.cpp
maybe_result_tests.cpp
)
target_include_directories(${TARGET}
PUBLIC $<TARGET_PROPERTY:maybe_result,INTERFACE_INCLUDE_DIRECTORIES>
)

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#define CATCH_CONFIG_MAIN
#include "catch.hpp"
/*
Exactly one source file must #define either CATCH_CONFIG_MAIN or CATCH_CONFIG_RUNNER before
#include-ing Catch.
In this file do not write any test cases!
In most cases that means this file will just contain two lines (the #define and the #include).
https://github.com/philsquared/Catch/blob/master/docs/tutorial.md
*/

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#include "catch.hpp"
#include <functional>
#include <maybe/result.hpp>
#include <memory>
#include <sstream>
using maybe::result;
class NoCopy final {
public:
NoCopy(NoCopy&& other)
{
flag = other.flag;
destructor_fun = std::move(other.destructor_fun);
other.destructor_fun = nullptr;
}
NoCopy& operator=(NoCopy&& other) = default;
NoCopy(int flag, std::function<void()> destructor_fun)
: flag(flag), destructor_fun(destructor_fun)
{
}
~NoCopy()
{
if (destructor_fun != nullptr) {
destructor_fun();
}
}
int get_flag()
{
return this->flag;
}
private:
int flag;
std::function<void()> destructor_fun;
};
TEST_CASE("maybe_result_tests")
{
SECTION("created ok result returns ok value")
{
auto res = result<int, int>::ok(12);
REQUIRE(res.is_ok());
REQUIRE(!res.is_err());
REQUIRE(res);
REQUIRE(res.ok_value() == 12);
auto other_ok = result<int, int>::ok(12);
REQUIRE(res == other_ok);
auto other_different_ok = result<int, int>::ok(42);
REQUIRE(res != other_different_ok);
}
SECTION("created err result returns err value")
{
auto res = result<int, int>::err(12);
REQUIRE(res.is_err());
REQUIRE(!res.is_ok());
REQUIRE(!res);
REQUIRE(res.err_value() == 12);
auto other_err = result<int, int>::err(12);
REQUIRE(res == other_err);
auto other_different_err = result<int, int>::err(42);
REQUIRE(res != other_different_err);
}
SECTION("created ok not equal created result")
{
auto ok = result<int, int>::ok(12);
auto err = result<int, int>::err(12);
REQUIRE(ok != err);
}
SECTION("throws exception if invalid value accessed")
{
auto ok = result<int, int>::ok(12);
auto err = result<int, int>::err(12);
REQUIRE_THROWS(ok.err_value());
REQUIRE_THROWS(err.ok_value());
}
SECTION("returns default values")
{
auto ok = result<int, int>::ok(12);
auto err = result<int, int>::err(12);
REQUIRE(ok.ok_value_or(42) == 12);
REQUIRE(err.err_value_or(42) == 12);
REQUIRE(ok.err_value_or(42) == 42);
REQUIRE(err.ok_value_or(42) == 42);
}
SECTION("destroys ok value correctly")
{
std::ostringstream ss;
{
result<NoCopy, NoCopy>::ok(NoCopy(0, [&] { ss << "[ok]"; }));
}
REQUIRE(ss.str() == "[ok]");
}
SECTION("destroys err value correctly")
{
std::ostringstream ss;
{
result<NoCopy, NoCopy>::err(NoCopy(0, [&] { ss << "[err]"; }));
}
REQUIRE(ss.str() == "[err]");
}
SECTION("nocopy ok to ok is moved correctly")
{
std::ostringstream ss;
{
auto val = result<NoCopy, NoCopy>::ok(NoCopy(0, [&] { ss << "[first]"; }));
val = result<NoCopy, NoCopy>::ok(NoCopy(42, [&] { ss << "[second]"; }));
REQUIRE(val.ok_value().get_flag() == 42);
}
REQUIRE(ss.str() == "[first][second]");
}
SECTION("nocopy err to err is moved correctly")
{
std::ostringstream ss;
{
auto val = result<NoCopy, NoCopy>::err(NoCopy(0, [&] { ss << "[first]"; }));
val = result<NoCopy, NoCopy>::err(NoCopy(42, [&] { ss << "[second]"; }));
REQUIRE(val.err_value().get_flag() == 42);
}
REQUIRE(ss.str() == "[first][second]");
}
SECTION("nocopy ok to err is moved correctly")
{
std::ostringstream ss;
{
auto val = result<NoCopy, NoCopy>::err(NoCopy(0, [&] { ss << "[first]"; }));
val = result<NoCopy, NoCopy>::ok(NoCopy(42, [&] { ss << "[second]"; }));
REQUIRE(val.ok_value().get_flag() == 42);
}
REQUIRE(ss.str() == "[first][second]");
}
SECTION("nocopy err to ok is moved correctly")
{
std::ostringstream ss;
{
auto val = result<NoCopy, NoCopy>::ok(NoCopy(0, [&] { ss << "[first]"; }));
val = result<NoCopy, NoCopy>::err(NoCopy(42, [&] { ss << "[second]"; }));
REQUIRE(val.err_value().get_flag() == 42);
}
REQUIRE(ss.str() == "[first][second]");
}
SECTION("nocopy ok to none is moved correctly")
{
std::ostringstream ss;
{
result<NoCopy, NoCopy> val;
val = result<NoCopy, NoCopy>::ok(NoCopy(42, [&] { ss << "[ok]"; }));
REQUIRE(val.ok_value().get_flag() == 42);
}
REQUIRE(ss.str() == "[ok]");
}
SECTION("nocopy err to none is moved correctly")
{
std::ostringstream ss;
{
result<NoCopy, NoCopy> val;
val = result<NoCopy, NoCopy>::err(NoCopy(42, [&] { ss << "[err]"; }));
REQUIRE(val.err_value().get_flag() == 42);
}
REQUIRE(ss.str() == "[err]");
}
}