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* [gcc/devel/rust/master] util: Add StackedContext class
@ 2022-07-28 15:35 Thomas Schwinge
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From: Thomas Schwinge @ 2022-07-28 15:35 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:0bf54ff468270dc60cb06dc1940e4bfb9e918c2b
commit 0bf54ff468270dc60cb06dc1940e4bfb9e918c2b
Author: Arthur Cohen <arthur.cohen@embecosm.com>
Date: Wed Jul 27 14:52:57 2022 +0200
util: Add StackedContext class
Diff:
---
gcc/rust/util/rust-stacked-contexts.h | 86 +++++++++++++++++++++++++++++++++++
1 file changed, 86 insertions(+)
diff --git a/gcc/rust/util/rust-stacked-contexts.h b/gcc/rust/util/rust-stacked-contexts.h
new file mode 100644
index 00000000000..c34eb907f06
--- /dev/null
+++ b/gcc/rust/util/rust-stacked-contexts.h
@@ -0,0 +1,86 @@
+// 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_CONTEXT_STACK_H
+#define RUST_CONTEXT_STACK_H
+
+#include "rust-system.h"
+
+namespace Rust {
+
+/**
+ * Context stack util class. This class is useful for situations where you can
+ * enter the same kind of context multiple times. For example, when dealing with
+ * unsafe contexts, you might be tempted to simply keep a boolean value.
+ *
+ * ```rust
+ * let a = 15;
+ * unsafe { // we set the boolean to true
+ * // Now unsafe operations are allowed!
+ * let b = *(&a as *const i32);
+ * let c = std::mem::transmute<i32, f32>(b); // Urgh!
+ * } // we set it to false
+ * ```
+ *
+ * However, since the language allows nested unsafe blocks, you may run into
+ * this situation:
+ *
+ * ```rust
+ * unsafe { // we set the boolean to true
+ * unsafe { // we set the boolean to true
+ * } // we set it to false
+ *
+ * // Now unsafe operations are forbidden again, the boolean is false
+ * let f = std::mem::transmute<i32, f32>(15); // Error!
+ * } // we set it to false
+ * ```
+ */
+template <typename T> class StackedContexts
+{
+public:
+ /**
+ * Enter a special context
+ */
+ void enter (T value) { stack.emplace_back (value); }
+
+ /**
+ * Exit a special context
+ */
+ T exit ()
+ {
+ rust_assert (!stack.empty ());
+
+ auto last = stack.back ();
+ stack.pop_back ();
+
+ return last;
+ }
+
+ /**
+ * Are we currently inside of a special context?
+ */
+ bool is_in_context () const { return !stack.empty (); }
+
+private:
+ /* Actual data */
+ std::vector<T> stack;
+};
+
+} // namespace Rust
+
+#endif /* !RUST_CONTEXT_STACK_H */
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