Replace `Maybe` with `std::optional` (#7005)

Because we are now using C++17, we can get rid of Maybe and instead
use std::optional, which offers the same functionality.

1 files changed, 26 insertions, 0 deletions

diff --git a/src/util/utility.h b/src/util/utility.h
index 3958ff166..9126d3e25 100644
--- a/src/util/utility.h
+++ b/src/util/utility.h
@@ -21,6 +21,7 @@
 #include <algorithm>
 #include <fstream>
 #include <memory>
+#include <optional>
 #include <string>
 
 namespace cvc5 {
@@ -61,6 +62,31 @@ void container_to_stream(std::ostream& out,
 }
 
 /**
+ * Generates a string representation of std::optional and inserts it into a
+ * stream.
+ *
+ * @param out The stream
+ * @param m The value
+ * @return The stream
+ */
+template <class T>
+std::ostream& operator<<(std::ostream& out, const std::optional<T>& m)
+{
+  out << "{";
+  if (m)
+  {
+    out << "Just ";
+    out << *m;
+  }
+  else
+  {
+    out << "Nothing";
+  }
+  out << "}";
+  return out;
+}
+
+/**
  * Opens a new temporary file with a given filename pattern and returns an
  * fstream to it. The directory that the file is created in is either TMPDIR or
  * /tmp/ if TMPDIR is not set.