C++ scripts

A .cpp script is a plain C++ file. It uses the same hot reload as a .hot script. This page is the overview of the .cpp script mode.

What a .cpp script is

A .cpp script holds a class that derives from a native engine class. The class has fields and methods. The host gives the path of the file to the engine, as it does for a .hot script.

The extension selects the parser:

• .hot selects the custom Hot++ syntax.
• .cpp selects libclang.

Both modes work in one program. A Loader holds one module for each generation, as for .hot scripts. Use one session for each script. There is no import between the modes. A .cpp script cannot include a .hot script. A .hot script cannot import a .cpp script.

The file compiles unchanged

A normal CMake build compiles a .cpp script with no hotc. Do not write #include "hot/script.h" in the script. The tool hotc injects hot/script.h itself. The header gives the macro HOT_ALIAS and the type hot::OldState.

The aids HOT_ALIAS, onReload and convert_* are temporary. Use them for a reload session. Remove them after the session. Then the file is standard C++ and a normal build compiles it with no extra option. The fixture tests/scripts/cpp_player_v1.cpp has no aids.

A normal build of a file that still has aids needs the header. Pass -include hot/script.h to the compiler, and add the include directory of Hot++ to the include path. The fixture tests/scripts/cpp_player_v2.cpp has aids. Its plain target cpp_scripts_plain2 does this.

In a normal build the file has plain C++ meaning. There is no state migration and there are no slots. Do not share objects between the two builds.

Coroutines

A .cpp script has no async word. A method can be a plain C++20 coroutine that returns hot::Task<T> and uses co_await and co_return. See Async and await for the task rules and the reload rules.

• A member coroutine of a script class has the reload guard. After a reload, a suspended task of the old generation ends with TaskReloadCancelled, and the task keeps its generation alive.
• A coroutine that is a free function or a lambda has no guard. Its frame can run old code after a reload, and it does not pin the generation.

The script build needs C++20.

Diagnostics

An error in a .cpp script shows the script file, the line, the column and the script text. The names keep the C++ spelling. See Diagnostics of a .cpp script.

Pages of this section

• Example: two generations of a .cpp script, and the CMake commands that build them.
• How hotc edits C++: the edits of a method body, lambdas and namespaces.
• Script classes: what a class can have, static members, definitions outside the class, member initializer lists, aliases and hooks.
• Types and inheritance: a script class as a type, casts, and script class inheritance.
• Limits and errors: the unsupported forms with the messages of hotc, and the known limits.