cast<T> function Null safety

Implementation

T cast<T>(dynamic input) {
  try {
    var typeString = T.toString();
    if (typeString.endsWith('?')) {
      if (input == null) {
        return null as T;
      } else {
        typeString = typeString.substring(0, typeString.length - 1);
      }
    }
    if (typeString.startsWith(_listPrefix)) {
      if (input is! List) {
        throw TypeError();
      }

      if (typeString.startsWith("List<int>")) {
        return List<int>.from(input) as T;
      } else if (typeString.startsWith("List<num>")) {
        return List<num>.from(input) as T;
      } else if (typeString.startsWith("List<double>")) {
        return List<double>.from(input) as T;
      } else if (typeString.startsWith("List<String>")) {
        return List<String>.from(input) as T;
      } else if (typeString.startsWith("List<bool>")) {
        return List<bool>.from(input) as T;
      } else if (typeString.startsWith("List<int?>")) {
        return List<int?>.from(input) as T;
      } else if (typeString.startsWith("List<num?>")) {
        return List<num?>.from(input) as T;
      } else if (typeString.startsWith("List<double?>")) {
        return List<double?>.from(input) as T;
      } else if (typeString.startsWith("List<String?>")) {
        return List<String?>.from(input) as T;
      } else if (typeString.startsWith("List<bool?>")) {
        return List<bool?>.from(input) as T;
      } else if (typeString.startsWith("List<Map<String, dynamic>>")) {
        return List<Map<String, dynamic>>.from(input) as T;
      } else if (typeString.startsWith("List<Map<String, dynamic>?>")) {
        return List<Map<String, dynamic>?>.from(input) as T;
      }
    } else if (typeString.startsWith(_mapPrefix)) {
      if (input is! Map) {
        throw TypeError();
      }

      final inputMap = input as Map<String, dynamic>;
      if (typeString.startsWith("Map<String, int>")) {
        return Map<String, int>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, num>")) {
        return Map<String, num>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, double>")) {
        return Map<String, double>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, String>")) {
        return Map<String, String>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, bool>")) {
        return Map<String, bool>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, int?>")) {
        return Map<String, int?>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, num?>")) {
        return Map<String, num?>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, double?>")) {
        return Map<String, double?>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, String?>")) {
        return Map<String, String?>.from(inputMap) as T;
      } else if (typeString.startsWith("Map<String, bool?>")) {
        return Map<String, bool?>.from(inputMap) as T;
      }
    }

    return input as T;
  } on TypeError catch (_) {
    throw TypeCoercionException(T, input.runtimeType);
  }
}