const_deferred_class

Deferred classes can't be created with 'const'.

The analyzer produces this diagnostic when a class from a library that is imported using a deferred import is used to create a const object. Constants are evaluated at compile time, and classes from deferred libraries aren't available at compile time.

For more information, check out Lazily loading a library.

The following code produces this diagnostic because it attempts to create a const instance of a class from a deferred library:

import 'dart:convert' deferred as convert;

const json2 = convert.JsonCodec();

If the object isn't required to be a constant, then change the code so that a non-constant instance is created:

import 'dart:convert' deferred as convert;

final json2 = convert.JsonCodec();

If the object must be a constant, then remove deferred from the import directive:

import 'dart:convert' as convert;

const json2 = convert.JsonCodec();

Unless stated otherwise, the documentation on this site reflects Dart 3.8.0. Page last updated on 2025-05-08. View source or report an issue.