First cut of pulling out the relevant parts of my original game to make a little framework.

src/dbc.hpp

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <string>
+#include <fmt/core.h>
+#include <functional>
+#include <source_location>
+
+// AKA the Fuckit macro
+#define $F(FMT, ...) fmt::format(FMT, ##__VA_ARGS__)
+
+namespace dbc {
+  using std::string;
+
+  class Error {
+    public:
+      const string message;
+      Error(string m) : message{m} {}
+      Error(const char *m) : message{m} {}
+  };
+
+  class CheckError : public Error {};
+  class SentinelError : public Error {};
+  class PreCondError : public Error {};
+  class PostCondError : public Error {};
+
+  void log(const string &message,
+      const std::source_location location =
+      std::source_location::current());
+
+  [[noreturn]] void sentinel(const string &message,
+      const std::source_location location =
+      std::source_location::current());
+
+  void pre(const string &message, bool test,
+      const std::source_location location =
+      std::source_location::current());
+
+  void pre(const string &message, std::function<bool()> tester,
+      const std::source_location location =
+      std::source_location::current());
+
+  void post(const string &message, bool test,
+      const std::source_location location =
+      std::source_location::current());
+
+  void post(const string &message, std::function<bool()> tester,
+      const std::source_location location =
+      std::source_location::current());
+
+  void check(bool test, const string &message,
+      const std::source_location location =
+      std::source_location::current());
+}