Socket values, enumerations, validators

The values of the input sockets are always stored as strings. They are only converted to real types at runtime, by the ng::Parser<T> of the data bank (see The runtime).

Attributes of a socket

Attribute	Sockets	Role
name	both	Displayed name.
id	both	Local ID in the node (see Identifiers).
type	both	Bit mask of the accepted types. Links require intersecting masks.
active	both	Stored and serialized, but not used by any logic yet.
callbacks on link added / broken	both	Qualifiers of callbacks (see Registries and self-registration).
value	input	Current value, used at runtime when the socket isn’t linked.
allowed_values	input	If not empty, the socket is an enumeration.
linkable	input	If false, the socket only accepts a constant value: add_link returns NotLinkable.
callbacks on value changed	input	Qualifiers of callbacks.

Checks done by Graph::set_socket_value

1. Allowed values (InputSocket::is_allowed_value): if the socket has a non-empty list of allowed values, the value must be one of them (case-sensitive). Otherwise NotAllowedValue. A socket without allowed values accepts anything.

2. Validators (InputSocket::check_validity): for each bit set in the socket’s type, the validator registered for that bit in ng::ValidatorsRegistry is looked up.

   • If no validator is registered for any of the socket’s types, the value is valid.

   • Otherwise, the value is valid if at least one of the registered validators accepts it. A socket Number | Text accepts “3” and “abc”.

   • A type without validator doesn’t make the value valid on its own: for Number | Unchecked, “abc” is refused because the Number validator refuses it.

   Otherwise InvalidValue.

3. The value is set and the “value changed” callbacks are triggered with the old value.

Note

InputSocket::set_value alone only checks the allowed values, not the validators. Always go through Graph::set_socket_value to change the value of a socket in a graph.

The default values given in a NodeDefinition are not checked: they should be valid for the socket’s validators, or the operator will fail to read them at runtime.

Registering a validator

constexpr ng::socket_t TYPE_NUMBER = ng::socket_t{1} << 0;

namespace {
    bool is_number(const std::string& value) { return ng::parse_from_string<double>(value).has_value(); }

    bool registered = ng::ValidatorsRegistry::instance().register_entry(TYPE_NUMBER, is_number);
}

Using the data bank’s parser as validator (like tests/elements/validators.cc) guarantees that every accepted value can be converted at runtime.