This is a prototype of what a deep cast package might look like.
Simple schema can be defined and used like this:
// Lists
const schema = cast.List(cast.int);
List<dynamic> someList = ....;
// Inferred type is List<String>, runtime reified type is List<String>
var typedList = schema.cast(someList); // Maps
const schema = cast.Map(cast.String, cast.int);
Map<dynamic, dynamic> someMap = ....;
// Inferred type is Map<String, int>, runtime reified type is Map<String, int>
var typedMap = schema.cast(someMap);Casts can be applied arbitrarily deep:
// Maps
const schema = cast.Map(cast.String, cast.List(cast.int));
Map<dynamic, dynamic> someMap = ....;
// Inferred type is Map<String, List<int>>,
// runtime reified type is Map<String, List<int>>
var typedMap = schema.cast(someMap);
// Inferred type is List<int>,
// runtime reified type is List<int>
var typedList = typedMap["field"];Complex schemas with different types for different fields can also be defined:
const typed = cast.Keyed<String, dynamic>({
"id": cast.int,
"fields": cast.Keyed({"field1": cast.int, "field2": cast.int}),
"extra1": cast.OneOf(cast.String, cast.List(cast.String)),
"extra2": cast.OneOf(cast.String, cast.List(cast.String)),
});Given structured data matching that schema:
var json = <String, dynamic>{
"id": 0,
"fields": <String, dynamic>{"field1": 1, "field2": 2},
"extra1": "hello",
"extra2": <dynamic>["hello"],
};Applying the cast gives back a deeply cast object of the right type:
Map<String, dynamic> result = typed.cast(json);
Map<String, int> fields = result["fields"]; // Implicit cast will not fail