class Details { final int cachedTokens; Details(this.cachedTokens); }
class Usage { final Details{{ optional }} details; final int totalTokens; Usage(this.details,this.totalTokens); }
class Chunk { final Usage? usage; Chunk(this.usage); }
void main() {
final chunks = [Chunk(Usage(Details(18),18))];
if ({{ expression }} != 18 || {{ standard }} != 18) { throw StateError('counter mismatch'); }
final absent = [Chunk(null)];
if ({{ absent }} != null) { throw StateError('missing usage'); }
}