Add optional_lookup utility function

This provides a more ergonomic interface over map::find

Author: hannes-steffenhagen-diffblue

src/util/optional_utils.h

@@ -0,0 +1,28 @@
+/*******************************************************************\
+
+ Module: functions that are useful with optionalt
+
+ Author: Diffblue Ltd.
+
+\*******************************************************************/
+
+#ifndef CPROVER_UTIL_OPTIONAL_UTILS_H
+#define CPROVER_UTIL_OPTIONAL_UTILS_H
+
+#include "optional.h"
+
+/// Lookup a key in a map, if found return the associated value,
+/// nullopt otherwise
+template <typename map_like_collectiont, typename keyt>
+auto optional_lookup(const map_like_collectiont &map, const keyt &key)
+  -> optionalt<decltype(map.find(key)->second)>
+{
+  auto const it = map.find(key);
+  if(it != map.end())
+  {
+    return it->second;
+  }
+  return nullopt;
+}
+
+#endif // CPROVER_UTIL_OPTIONAL_UTILS_H

unit/util/optional_utils.cpp

@@ -0,0 +1,44 @@
+/*******************************************************************\
+
+ Module: optional_utils unit tests
+
+ Author: Diffblue Ltd.
+
+\*******************************************************************/
+
+#include <testing-utils/catch.hpp>
+
+#include <util/optional_utils.h>
+
+#include <map>
+#include <string>
+#include <unordered_map>
+
+namespace
+{
+template <typename map_like_collectiont>
+void do_optional_lookup_test(map_like_collectiont &map)
+{
+  map.insert({"hello", "world"});
+  map.insert({"pwd", "/home"});
+  auto const hello_result = optional_lookup(map, "hello");
+  REQUIRE(hello_result.has_value());
+  REQUIRE(hello_result.value() == "world");
+  auto const pwd_result = optional_lookup(map, "pwd");
+  REQUIRE(pwd_result.has_value());
+  REQUIRE(pwd_result.value() == "/home");
+  REQUIRE_FALSE(optional_lookup(map, "does not exit").has_value());
+}
+} // namespace
+
+TEST_CASE("Using optional_lookup with std::map")
+{
+  auto map = std::map<std::string, std::string>{};
+  do_optional_lookup_test(map);
+}
+
+TEST_CASE("Using optional_lookup with std::unordered_map")
+{
+  auto map = std::unordered_map<std::string, std::string>{};
+  do_optional_lookup_test(map);
+}