Can an instance type be separated from value creation?

Question

In C ++, I can create an instance of a generic type at compile time, and then build it at runtime:

struct Vertex {};
struct Edge   {};

template<typename NodeType, typename IdType>
struct Wrapper {
  IdType id;

  Wrapper(IdType id) : id{id} {};
};

int main() {
  using vertexWrapper = Wrapper<Vertex, int>;
  vertexWrapper v(3);
}

Variables are clearly separated and types never look / don't look like values. I am trying to do something like this in the Chapel:

record Vertex {}
record Edge   {}

record Wrapper {
  type nodeType;
  type idType;   
  var id: idType;

  proc init(id) {
    this.id = id;
  }
}

type vertexWrapper = Wrapper(Vertex, int);

var v1 = 3: vertexWrapper;

When I compile this code, I get:

chpl -o graph-add-inclusion --cc-warnings test.chpl
test.chpl:9: In initializer:
test.chpl:10: error: can't omit initialization of field "nodeType", no type or default value provided
test.chpl:10: error: can't omit initialization of field "idType", no type or default value provided

Is there a way to separate type construction from value construction in the Chapel in order to achieve the effect of the tagged type that I am trying to get in my example? I use tagged types to have a single implementation that is common to two types of entities (vertices and edges here), but I want these objects to be different types.

There is one more related question. Should I just write:

type vertexWrapper = Wrapper(Vertex);

and then the integer is output separately from my constructor?

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Answer 1

, , , , , . - , , :

var x = new Wrapper(1); // type is inferred from the new return

, nodeType idType. .

, , , , , , . , , .

, idType .

proc init(id) {
  idType = id.type;
  this.id = id;
}

nodeType, , , . , . , nodeType:

var v1 = new vertexWrapper(vertexWrapper.nodeType, 3);

, . v1 :

record Vertex {}
record Edge   {}

record Wrapper {
  type nodeType;
  type idType;   
  var id: idType;

  proc init(type nodeType, id) {
    this.nodeType = nodeType;
    this.idType = id.type;
    this.id = id;
  }
}

type vertexWrapper = Wrapper(Vertex, int);

var v1 = new vertexWrapper(vertexWrapper.nodeType, 3);

, , .

:

type vertexWrapper = Wrapper(Vertex);

?

, Wrapper(Vertex) , . , idType int, :

type idType = int;

nodeType Wrapper(Vertex), , idType int, new (var x = new Wrapper(Vertex, 3.0);), - , nodeType.

Answer 2

(, ), , Chapel , , , .

, , , , [Try It Online]. , factory, newNode() Wrapper, type-i.e., , :

record Vertex {}
record Edge   {}

record Wrapper {
  type nodeType;
  type idType;
  var id: idType;

  proc type newNode(id) {
    return new Wrapper(nodeType, idType, id);
  }
}

type vertexWrapper = Wrapper(Vertex, int);

var v1 = vertexWrapper.newNode(3);
writeln(v1);

vertexWrapper nodeType, factory, Wrapper.

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