From 21f8c0d1d68b370f25e6097ae61c0169e13940a7 Mon Sep 17 00:00:00 2001
From: Matthias Maier <tamiko@43-1.org>
Date: Sun, 29 Oct 2023 17:07:03 -0500
Subject: [PATCH] base/memory_consumption.h: add specialization for
 std::optional<T>

---
 include/deal.II/base/memory_consumption.h | 34 +++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/include/deal.II/base/memory_consumption.h b/include/deal.II/base/memory_consumption.h
index e37784d155..0f2f362925 100644
--- a/include/deal.II/base/memory_consumption.h
+++ b/include/deal.II/base/memory_consumption.h
@@ -24,6 +24,7 @@
 #include <cstddef>
 #include <cstring>
 #include <memory>
+#include <optional>
 #include <string>
 #include <type_traits>
 #include <vector>
@@ -220,6 +221,14 @@ namespace MemoryConsumption
   inline std::size_t
   memory_consumption(const std::pair<A, B> &p);
 
+  /**
+   * Determine an estimate of the amount of memory in bytes consumed by a
+   * value wrapped in a std::optional.
+   */
+  template <typename A>
+  inline std::size_t
+  memory_consumption(const std::optional<A> &o);
+
   /**
    * Calculate the memory consumption of a pointer.
    *
@@ -380,6 +389,31 @@ namespace MemoryConsumption
 
 
 
+  template <typename A>
+  inline std::size_t
+  memory_consumption(const std::optional<A> &o)
+  {
+    if (o.has_value())
+      {
+        //
+        // If the optional carries a value then we query the contained
+        // value for memory consumption and estimate the size of the
+        // control overhead.
+        //
+        return memory_consumption(o.value()) + sizeof(o) - sizeof(A);
+      }
+    else
+      {
+        //
+        // The optional contains no value, so simply return its plain size
+        // (consisting of space for the value and control overhead):
+        //
+        return sizeof(o);
+      }
+  }
+
+
+
   template <typename T>
   inline std::size_t
   memory_consumption(const T *const)
-- 
2.39.5