cmConstStack: Factor out of cmListFileBacktrace

This presents value semantics for a stack of constant values.
Internally it shares ownership to avoid copies.  Previously
this was implemented by `cmListFileBacktrace` explicitly,
but the approach can be re-used for other kinds of stacks.

1 files changed, 62 insertions, 0 deletions

diff --git a/Source/cmConstStack.tcc b/Source/cmConstStack.tcc
new file mode 100644
index 0000000..81918ee
--- /dev/null
+++ b/Source/cmConstStack.tcc
@@ -0,0 +1,62 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#include <cassert>
+#include <memory>
+#include <utility>
+
+template <typename T, typename Stack>
+struct cmConstStack<T, Stack>::Entry
+{
+  Entry(std::shared_ptr<Entry const> parent, T value)
+    : Value(std::move(value))
+    , Parent(std::move(parent))
+  {
+  }
+
+  T Value;
+  std::shared_ptr<Entry const> Parent;
+};
+
+template <typename T, typename Stack>
+cmConstStack<T, Stack>::cmConstStack() = default;
+
+template <typename T, typename Stack>
+Stack cmConstStack<T, Stack>::Push(T value) const
+{
+  return Stack(this->TopEntry, std::move(value));
+}
+
+template <typename T, typename Stack>
+Stack cmConstStack<T, Stack>::Pop() const
+{
+  assert(this->TopEntry);
+  return Stack(this->TopEntry->Parent);
+}
+
+template <typename T, typename Stack>
+T const& cmConstStack<T, Stack>::Top() const
+{
+  assert(this->TopEntry);
+  return this->TopEntry->Value;
+}
+
+template <typename T, typename Stack>
+bool cmConstStack<T, Stack>::Empty() const
+{
+  return !this->TopEntry;
+}
+
+template <typename T, typename Stack>
+cmConstStack<T, Stack>::cmConstStack(std::shared_ptr<Entry const> parent,
+                                     T value)
+  : TopEntry(
+      std::make_shared<Entry const>(std::move(parent), std::move(value)))
+{
+}
+
+template <typename T, typename Stack>
+cmConstStack<T, Stack>::cmConstStack(std::shared_ptr<Entry const> top)
+  : TopEntry(std::move(top))
+{
+}