When using opImplConv to bool and then checking an instance of the type in a ternary operator condition a compiler error is given:

Expression must be of boolean type

It does work when used in an if statement, so this seems like an oversight.

Registration code:

class Scheduler
{
public:
	struct ScheduledFunction {};

	struct ScheduledFunctionHandle
	{
		ScheduledFunction* Function{};
		std::chrono::system_clock::time_point CreationTime{};
	};
};

static void ConstructScheduledFunctionHandle(void* memory)
{
	new (memory) Scheduler::ScheduledFunctionHandle();
}

static void DestructScheduledFunctionHandle(Scheduler::ScheduledFunctionHandle* handle)
{
	handle->~ScheduledFunctionHandle();
}

static void CopyConstructScheduledFunctionHandle(void* memory, const Scheduler::ScheduledFunctionHandle& other)
{
	new (memory) Scheduler::ScheduledFunctionHandle(other);
}

static bool ScheduledFunction_opImplConv(const Scheduler::ScheduledFunctionHandle* handle)
{
	return handle->Function != nullptr;
}

static void RegisterScheduledFunction(asIScriptEngine& engine)
{
	const char* const name = "ScheduledFunction";

	engine.RegisterObjectType(name, sizeof(Scheduler::ScheduledFunctionHandle), asOBJ_VALUE | asGetTypeTraits<Scheduler::ScheduledFunctionHandle>());

	engine.RegisterObjectBehaviour(name, asBEHAVE_CONSTRUCT, "void f()",
		asFUNCTION(ConstructScheduledFunctionHandle), asCALL_CDECL_OBJFIRST);

	engine.RegisterObjectBehaviour(name, asBEHAVE_DESTRUCT, "void f()",
		asFUNCTION(DestructScheduledFunctionHandle), asCALL_CDECL_OBJFIRST);

	engine.RegisterObjectBehaviour(name, asBEHAVE_CONSTRUCT, "void f(const ScheduledFunction& in other)",
		asFUNCTION(CopyConstructScheduledFunctionHandle), asCALL_CDECL_OBJFIRST);

	engine.RegisterObjectMethod(name, "ScheduledFunction& opAssign(const ScheduledFunction& in other)",
		asMETHODPR(Scheduler::ScheduledFunctionHandle, operator=, (const Scheduler::ScheduledFunctionHandle&), Scheduler::ScheduledFunctionHandle&),
		asCALL_THISCALL);

	engine.RegisterObjectMethod(name, "bool opImplConv() const",
		asFUNCTION(ScheduledFunction_opImplConv), asCALL_CDECL_OBJFIRST);
}

Script code:

ScheduledFunction sched;
Print("Scheduled function handle is valid: " + sched ? "yes" : "no" + "\n");

That does work. Sorry about that, the error message seemed to indicate that it was the implicit conversion that wasn't working. Looks like it's implicitly converting the value type to bool, calling opAdd and then trying to evaluate the result? Allowing implicit operator+ with bool seems like it could cause problems, i'd use an explicit conversion like C++'s to_string overloads.

I meant that it should not be possible to do this:

string str = "this is a string: " + true;

The default string addon allows this, but i'm suggesting it should require this:

string str = "this is a string: " + to_string(true);

Alright, thanks. It would be great if such a macro could disable all implicit conversions (i.e. only other strings can be used with the string API) to harden against accidental conversions.