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From: arthur.cohen@embecosm.com
To: gcc-patches@gcc.gnu.org
Cc: gcc-rust@gcc.gnu.org, Arthur Cohen <arthur.cohen@embecosm.com>
Subject: [PATCH Rust front-end v4 24/46] gccrs: Add implementation of Optional
Date: Tue,  6 Dec 2022 11:13:56 +0100	[thread overview]
Message-ID: <20221206101417.778807-25-arthur.cohen@embecosm.com> (raw)
In-Reply-To: <20221206101417.778807-1-arthur.cohen@embecosm.com>

From: Arthur Cohen <arthur.cohen@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


  parent reply	other threads:[~2022-12-06 10:12 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-06 10:13 Rust front-end patches v4 arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 01/46] Use DW_ATE_UTF for the Rust 'char' type arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 02/46] gccrs: Add necessary hooks for a Rust front-end testsuite arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 03/46] gccrs: Add Debug info testsuite arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 04/46] gccrs: Add link cases testsuite arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 05/46] gccrs: Add general compilation test cases arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 06/46] gccrs: Add execution " arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 07/46] gccrs: Add gcc-check-target check-rust arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 08/46] gccrs: Add Rust front-end base AST data structures arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 09/46] gccrs: Add definitions of Rust Items in " arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 10/46] gccrs: Add full definitions of Rust " arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 11/46] gccrs: Add Rust AST visitors arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 12/46] gccrs: Add Lexer for Rust front-end arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 13/46] gccrs: Add Parser for Rust front-end pt.1 arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 14/46] gccrs: Add Parser for Rust front-end pt.2 arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 15/46] gccrs: Add expansion pass for the Rust front-end arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 16/46] gccrs: Add name resolution pass to " arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 17/46] gccrs: Add declarations for Rust HIR arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 18/46] gccrs: Add HIR definitions and visitor framework arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 19/46] gccrs: Add AST to HIR lowering pass arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 20/46] gccrs: Add wrapper for make_unique arthur.cohen
2022-12-07  8:50   ` Arsen Arsenović
2022-12-07  9:14     ` Thomas Schwinge
2022-12-06 10:13 ` [PATCH Rust front-end v4 21/46] gccrs: Add port of FNV hash used during legacy symbol mangling arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 22/46] gccrs: Add Rust ABI enum helpers arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 23/46] gccrs: Add Base62 implementation arthur.cohen
2022-12-06 10:13 ` arthur.cohen [this message]
2022-12-06 10:13 ` [PATCH Rust front-end v4 25/46] gccrs: Add attributes checker arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 26/46] gccrs: Add helpers mappings canonical path and lang items arthur.cohen
2022-12-06 10:13 ` [PATCH Rust front-end v4 27/46] gccrs: Add type resolution and trait solving pass arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 28/46] gccrs: Add Rust type information arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 29/46] gccrs: Add remaining type system transformations arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 30/46] gccrs: Add unsafe checks for Rust arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 31/46] gccrs: Add const checker arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 32/46] gccrs: Add privacy checks arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 33/46] gccrs: Add dead code scan on HIR arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 34/46] gccrs: Add unused variable scan arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 35/46] gccrs: Add metadata output pass arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 36/46] gccrs: Add base for HIR to GCC GENERIC lowering arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 37/46] gccrs: Add HIR to GCC GENERIC lowering for all nodes arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 38/46] gccrs: Add HIR to GCC GENERIC lowering entry point arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 39/46] gccrs: These are wrappers ported from reusing gccgo arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 40/46] gccrs: Add GCC Rust front-end Make-lang.in arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 41/46] gccrs: Add config-lang.in arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 42/46] gccrs: Add lang-spec.h arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 43/46] gccrs: Add lang.opt arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 44/46] gccrs: Add compiler driver arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 45/46] gccrs: Compiler proper interface kicks off the pipeline arthur.cohen
2022-12-06 10:14 ` [PATCH Rust front-end v4 46/46] gccrs: Add README, CONTRIBUTING and compiler logo arthur.cohen
2022-12-09 10:18   ` Martin Liška
2022-12-13  1:43     ` Joseph Myers
2022-12-13 12:59       ` Martin Liška
2022-12-13 18:46         ` Joseph Myers
2022-12-06 11:03 ` Rust front-end patches v4 Richard Biener
2022-12-06 11:09   ` John Paul Adrian Glaubitz
2022-12-06 11:40     ` Arthur Cohen
2022-12-06 11:57       ` John Paul Adrian Glaubitz
2022-12-06 12:40         ` Mark Wielaard
2022-12-06 11:41   ` Iain Buclaw
2022-12-10  6:39   ` Prepare 'contrib/gcc-changelog/git_commit.py' for GCC/Rust (was: Rust front-end patches v4) Thomas Schwinge
2022-12-10  7:37     ` Add stub 'gcc/rust/ChangeLog' (was: Prepare 'contrib/gcc-changelog/git_commit.py' for GCC/Rust) Thomas Schwinge
2022-12-13 13:26   ` Rust front-end patches v4 Arthur Cohen
2022-12-13 13:30     ` Martin Liška
2022-12-13 13:53       ` Arthur Cohen
2022-12-13 13:40     ` Arthur Cohen
2022-12-14 22:58       ` Make '-frust-incomplete-and-experimental-compiler-do-not-use' a 'Common' option (was: Rust front-end patches v4) Thomas Schwinge
2022-12-15  7:53         ` Richard Biener
2022-12-15 10:14           ` Thomas Schwinge
2022-12-15 11:16             ` Jakub Jelinek
2022-12-15 11:39               ` Iain Buclaw
2022-12-15 11:50                 ` Jakub Jelinek
2022-12-15 15:01                   ` Thomas Schwinge
2022-12-15 15:17                     ` Jakub Jelinek
2022-12-16 14:10                       ` Add '-Wno-complain-wrong-lang', and use it in 'gcc/testsuite/lib/target-supports.exp:check_compile' and elsewhere (was: Make '-frust-incomplete-and-experimental-compiler-do-not-use' a 'Common' option) Thomas Schwinge
2022-12-16 21:24                         ` Iain Buclaw
2023-01-11 11:41                         ` [PING] Add '-Wno-complain-wrong-lang', and use it in 'gcc/testsuite/lib/target-supports.exp:check_compile' and elsewhere Thomas Schwinge
2023-01-11 12:31                           ` Jakub Jelinek
2023-02-21 10:21                             ` [PING, v2] " Thomas Schwinge
2023-02-21 23:20                               ` Joseph Myers
2022-12-09 13:24 ` Rust front-end patches v4 Martin Liška
2022-12-10 21:44   ` Thomas Schwinge

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