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Handling lua::error

lua::error is Luacxx's main exception type for failures that occur while working with Lua.

It is used for things like:

  • Lua syntax errors
  • Lua runtime errors
  • type/conversion failures
  • Luacxx API checks that are fundamentally about Lua values

Why It Exists

Lua itself reports many failures through the C API and the Lua stack. Luacxx converts those failures into a normal C++ exception type so they can be handled with ordinary try / catch.

try {
    lua::run_string(env, "error('Intentional')");
} catch (const lua::error& ex) {
    std::cerr << ex.what() << '\n';
}

Message And Traceback

lua::error stores both the main message and, when available, a traceback.

The key methods are:

  • what()
  • message()
  • traceback()
  • set_traceback(...)

what() returns the full stored string. message() returns just the main error text without the traceback suffix.

Constructing One Yourself

You can throw a lua::error directly from C++ binding code:

if (lua_type(state, 1) != LUA_TFUNCTION) {
    throw lua::error("A function was expected");
}

There is also a constructor that accepts a lua_State*, which Luacxx uses when building richer messages from the current Lua context.

What Should Throw lua::error

As a rule of thumb, lua::error is appropriate when the failure is naturally part of using Lua:

  • bad Lua code
  • wrong Lua value type
  • invalid Lua call target
  • conversion failure

For purely host-side issues such as unrelated C++ logic failures, ordinary C++ exception types may still be more appropriate.

Catching Errors Around Lua Calls

This is the common pattern:

try {
    int answer = lua::call<int>(env["compute"], 2, 3);
} catch (const lua::error& ex) {
    std::cerr << "Lua call failed: " << ex.message() << '\n';
    if (!ex.traceback().empty()) {
        std::cerr << ex.traceback() << '\n';
    }
}

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