How to get the subtypes of a generic type using `DartType` from `analyzer` package?

Issue

How can I get the subtypes of an element using the class DartType from the analyzer package?

for example if the type is List<String>, I would like to get String. Also will be useful to get if the type is generic.

Another more complex example would be Map<String, String> where I want to get a list of the subtypes, in this case: [String, String].

Solution

This one is a little tricky – because DartType actually itself has some super types – the one that will interest you here is ParameterizedType:

import 'package:analyzer/dart/element/type.dart';

Iterable<DartType> getGenericTypes(DartType type) {
  return type is ParameterizedType ? type.typeArguments : const [];
}

I don’t know if it’s possible to know if the type is generic – after all, it’s just a type. But you can check if the type accepts generic parameters, again, using ClassElement:

import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/type.dart';

bool canHaveGenerics(DartType type) {
  final element = type.element;
  if (element is ClassElement) {
    return element.typeParameters.isNotEmpty;
  }
  return false;
}

Hope that helps!

Answered By – matanlurey

Answer Checked By – Marie Seifert (FlutterFixes Admin)