The purpose of this class is much like Emacs' (interactive) form: it
allows a value expression function to declare exactly how many
arguments, and of what type, it intends to receive. It then offers
type-safe access to theese arguments in a consistent manner.
An example value expression function definition in C++:
value_t fn_foo(call_scope_t& scope) {
// We expect a string, an integer, and an optional date
interactive_t args(scope, "sl&d");
std::cout << "String = " << args.get<string>(0)
<< "Integer = " << args.get<long>(1) << std::endl;
if (args.has(2)) // was a date provided?
std::cout << "Date = " << args.get<date_t>(2) << std::endl;
return NULL_VALUE;
}
There is also an in_context_t<T> template, which finds the context type
T in the current scope hierarchy. The in_context_t then also acts as a
smart pointer to reference this context object, in addition to serving
the same duty as interactive_t. This combination of intent is solely
for the sake of brevity.
value_t fn_bar(call_scope_t& scope) {
in_context_t<account_t> env(scope, "sl&d");
std::cout << "Account name = " << env->fullname()
<< "String arg = " << env.get<string>(0)
<< std::endl;
return NULL_VALUE;
}
As you can see here, 'env' acts as a smart pointer to the required
context, and an object to extract the typed arguments.
