Move gdbsupport to the top level

[deliverable/binutils-gdb.git] / gdbsupport / default-init-alloc.h

diff --git a/gdbsupport/default-init-alloc.h b/gdbsupport/default-init-alloc.h
new file mode 100644 (file)
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+++ b/gdbsupport/default-init-alloc.h
@@ -0,0 +1,67 @@
+/* Copyright (C) 2017-2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program 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 of the License, or
+   (at your option) any later version.
+
+   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef COMMON_DEFAULT_INIT_ALLOC_H
+#define COMMON_DEFAULT_INIT_ALLOC_H
+
+namespace gdb {
+
+/* An allocator that default constructs using default-initialization
+   rather than value-initialization.  The idea is to use this when you
+   don't want to default construct elements of containers of trivial
+   types using zero-initialization.  */
+
+/* Mostly as implementation convenience, this is implemented as an
+   adapter that given an allocator A, overrides 'A::construct()'.  'A'
+   defaults to std::allocator<T>.  */
+
+template<typename T, typename A = std::allocator<T>>
+class default_init_allocator : public A
+{
+public:
+  /* Pull in A's ctors.  */
+  using A::A;
+
+  /* Override rebind.  */
+  template<typename U>
+  struct rebind
+  {
+    /* A couple helpers just to make it a bit more readable.  */
+    typedef std::allocator_traits<A> traits_;
+    typedef typename traits_::template rebind_alloc<U> alloc_;
+
+    /* This is what we're after.  */
+    typedef default_init_allocator<U, alloc_> other;
+  };
+
+  /* Make the base allocator's construct method(s) visible.  */
+  using A::construct;
+
+  /* .. and provide an override/overload for the case of default
+     construction (i.e., no arguments).  This is where we construct
+     with default-init.  */
+  template <typename U>
+  void construct (U *ptr)
+    noexcept (std::is_nothrow_default_constructible<U>::value)
+  {
+    ::new ((void *) ptr) U; /* default-init */
+  }
+};
+
+} /* namespace gdb */
+
+#endif /* COMMON_DEFAULT_INIT_ALLOC_H */