Unique id of the node class used in serialization of ErgoTree.
Every value represents an operation and that operation can be associated with a function type, describing functional meaning of the operation, kind of operation signature.
Every value represents an operation and that operation can be associated with a function type, describing functional meaning of the operation, kind of operation signature. Thus we can obtain global operation identifiers by combining Value.opName with Value.opType, so that if (v1.opName == v2.opName) && (v1.opType == v2.opType) then v1 and v2 are functionally point-wise equivalent. This in particular means that if two _different_ ops have the same opType they _should_ have different opNames. Thus defined op ids are used in a Cost Model - a table of all existing primitives coupled with performance parameters.
The type of the value represented by this node.