From: Arthur Cohen <arthur.co...@embecosm.com> This adds an Optional<T> class to improve error handling. --- gcc/rust/util/rust-optional-test.cc | 110 +++++++++++ gcc/rust/util/rust-optional.h | 278 ++++++++++++++++++++++++++++ 2 files changed, 388 insertions(+) create mode 100644 gcc/rust/util/rust-optional-test.cc create mode 100644 gcc/rust/util/rust-optional.h
diff --git a/gcc/rust/util/rust-optional-test.cc b/gcc/rust/util/rust-optional-test.cc new file mode 100644 index 00000000000..43fa175fa40 --- /dev/null +++ b/gcc/rust/util/rust-optional-test.cc @@ -0,0 +1,110 @@ +// Copyright (C) 2020-2022 Free Software Foundation, Inc. + +// This file is part of GCC. + +// GCC is free software; you can redistribute it and/or modify it under +// the terms of the GNU General Public License as published by the Free +// Software Foundation; either version 3, or (at your option) any later +// version. + +// GCC is distributed in the hope that it will be useful, but WITHOUT ANY +// WARRANTY; without even the implied warranty of MERCHANTABILITY or +// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License +// for more details. + +// You should have received a copy of the GNU General Public License +// along with GCC; see the file COPYING3. If not see +// <http://www.gnu.org/licenses/>. + +#include "rust-system.h" +#include "rust-optional.h" +#include "selftest.h" + +#if CHECKING_P + +static void +rust_optional_create () +{ + auto opt = Rust::Optional<int>::some (15); + + ASSERT_TRUE (opt.is_some ()); + ASSERT_EQ (opt.get (), 15); + + Rust::Optional<int> const_opt = Rust::Optional<int>::some (15); + const int &value = const_opt.get (); + + ASSERT_EQ (value, 15); +} + +static void +rust_optional_operators () +{ + auto opt = Rust::Optional<int>::some (15); + + // as bool + ASSERT_TRUE (opt); + + // deref + ASSERT_EQ (*opt, 15); + + class Methodable + { + public: + int method () { return 15; } + }; + + auto m_opt = Rust::Optional<Methodable>::some (Methodable ()); + ASSERT_EQ (m_opt->method (), 15); +} + +static void +rust_optional_take () +{ + auto opt = Rust::Optional<int>::some (15); + auto value = opt.take (); + + ASSERT_EQ (value, 15); + ASSERT_TRUE (opt.is_none ()); +} + +static void +rust_optional_map () +{ + auto opt = Rust::Optional<int>::some (15); + auto twice = opt.map<int> ([] (int value) { return value * 2; }); + + ASSERT_FALSE (opt); + ASSERT_TRUE (twice); + ASSERT_EQ (*twice, 30); +} + +static void +rust_optional_reference () +{ + auto value = std::vector<std::string> (); + value.emplace_back ("rust"); + value.emplace_back ("+"); + value.emplace_back ("gcc"); + value.emplace_back ("="); + value.emplace_back ("<3"); + + auto opt = Rust::Optional<std::vector<std::string> &>::some (value); + + ASSERT_EQ (opt->at (0), "rust"); + ASSERT_EQ (opt->at (2), "gcc"); +} + +#endif /* #if CHECKING_P */ + +void +rust_optional_test () +{ +#if CHECKING_P + rust_optional_create (); + rust_optional_operators (); + rust_optional_take (); + rust_optional_map (); + rust_optional_reference (); + +#endif /* #if CHECKING_P */ +} diff --git a/gcc/rust/util/rust-optional.h b/gcc/rust/util/rust-optional.h new file mode 100644 index 00000000000..56465400250 --- /dev/null +++ b/gcc/rust/util/rust-optional.h @@ -0,0 +1,278 @@ +// Copyright (C) 2020-2022 Free Software Foundation, Inc. + +// This file is part of GCC. + +// GCC is free software; you can redistribute it and/or modify it under +// the terms of the GNU General Public License as published by the Free +// Software Foundation; either version 3, or (at your option) any later +// version. + +// GCC is distributed in the hope that it will be useful, but WITHOUT ANY +// WARRANTY; without even the implied warranty of MERCHANTABILITY or +// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License +// for more details. + +// You should have received a copy of the GNU General Public License +// along with GCC; see the file COPYING3. If not see +// <http://www.gnu.org/licenses/>. + +#ifndef RUST_OPTIONAL_H +#define RUST_OPTIONAL_H + +#include "config.h" +#include "rust-system.h" + +#include "selftest.h" + +namespace Rust { + +/** + * Tagged union to try and simulate a sum type. This is safer and more ergonomic + * than one of the two alternatives we're currently using in the compiler: + * + * 1. Storing a raw pointer, which can be `nullptr` or valid + * + * This is wildly unsafe, and usable in conjunction with local references, stack + * variables, or pointers managed elsewhere, which can cause crashes, hard to + * debug issues or undefined behavior. Likewise, if you do not check for the + * pointer's validity, this will cause a crash. + * + * 2. Storing an extra boolean alongside the object + * + * This causes implementors to use a "dummy object": Either an empty version or + * an error version. But what happens if what you really wanted to store was + * the empty or error version? You can also easily incorporate logic bugs if you + * forget to check for the associated boolean. + * + * The `Optional<T>` type has the same "ergonomic" cost: You need to check + * whether your option is valid or not. However, the main advantage is that it + * is more restrictive: You can only acess the member it contains "safely". + * It is similar to storing a value + an associated boolean, but has the + * advantage of making up only one member in your class. + * You also benefit from some helper methods such as `map()`. + * + * You also get helper functions and operator overloading to "seamlessly" + * replace raw pointer alternatives. + * + * ```c++ + * MyType *raw_pointer = something_that_can_fail(); + * if (raw_pointer) + * raw_pointer->method(); + * + * // or + * + * Optional<MyType> opt = something_that_can_fail2(); + * if (opt) + * opt->method(); + * + * // equivalent to + * + * if (opt.is_some()) + * opt.get().method(); + * ``` + */ +template <typename T> class Optional +{ +private: + struct Empty + { + }; + + enum Kind + { + Some, + None + } kind; + + union Content + { + Empty empty; + T value; + + Content () = default; + } content; + + Optional<T> (Kind kind, Content content) : kind (kind), content (content) {} + +public: + Optional (const Optional &other) = default; + Optional &operator= (const Optional &other) = default; + Optional (Optional &&other) = default; + + static Optional<T> some (T value) + { + Content content; + content.value = value; + + return Optional (Kind::Some, content); + } + + static Optional<T> none () + { + Content content; + content.empty = Empty (); + + return Optional (Kind::None, content); + } + + bool is_some () const { return kind == Kind::Some; } + bool is_none () const { return !is_some (); } + + /** + * Enable boolean-like comparisons. + */ + operator bool () { return is_some (); } + + /** + * Enables dereferencing to access the contained value + */ + T &operator* () { return get (); } + const T &operator* () const { return get (); } + T *operator-> () { return &get (); } + const T *operator-> () const { return &get (); } + + const T &get () const + { + rust_assert (is_some ()); + + return content.value; + } + + T &get () + { + rust_assert (is_some ()); + + return content.value; + } + + T take () + { + rust_assert (is_some ()); + + auto to_return = std::move (content.value); + + content.empty = Empty (); + kind = Kind::None; + + return to_return; + } + + template <typename U> Optional<U> map (std::function<U (T)> functor) + { + if (is_none ()) + return Optional::none (); + + auto value = functor (take ()); + + return Optional::some (value); + } +}; + +template <typename T> class Optional<T &> +{ +private: + struct Empty + { + }; + + enum Kind + { + Some, + None + } kind; + + union Content + { + Empty empty; + T *value; + + Content () = default; + } content; + + Optional<T &> (Kind kind, Content content) : kind (kind), content (content) {} + +public: + Optional (const Optional &other) = default; + Optional (Optional &&other) = default; + + static Optional<T &> some (T &value) + { + Content content; + content.value = &value; + + return Optional (Kind::Some, content); + } + + static Optional<T &> none () + { + Content content; + content.empty = Empty (); + + return Optional (Kind::None, content); + } + + bool is_some () const { return kind == Kind::Some; } + bool is_none () const { return !is_some (); } + + // FIXME: Can we factor this in a single class? + + /** + * Enable boolean-like comparisons. + */ + operator bool () { return is_some (); } + + /** + * Enables dereferencing to access the contained value + */ + T &operator* () { return get (); } + const T &operator* () const { return get (); } + T *operator-> () { return &get (); } + const T *operator-> () const { return &get (); } + + const T &get () const + { + rust_assert (is_some ()); + + return *content.value; + } + + T &get () + { + rust_assert (is_some ()); + + return *content.value; + } + + T &take () + { + rust_assert (is_some ()); + + auto to_return = std::move (content.value); + + content.empty = Empty (); + kind = Kind::None; + + return *to_return; + } + + template <typename U> Optional<U &> map (std::function<U &(T &)> functor) + { + if (is_none ()) + return Optional::none (); + + auto value = functor (take ()); + + return Optional::some (value); + } +}; + +} // namespace Rust + +#ifdef CHECKING_P + +void +rust_optional_test (); + +#endif // !CHECKING_P + +#endif // !RUST_OPTIONAL_H -- 2.38.1
