# global Class -> Size map, mutable
class-to-size-index := (: BTreeEqEOF BTreeEq<String,U64>);

index-size-of-class := λ(: class String)(: size U64). (: (
   (.bind( (as (& class-to-size-index) BTreeEq<String,U64>[]) class size ))
) Nil);

size-of-class := λ(: class String). (: (
   (.lookup( class-to-size-index class 0_u64 ))
) U64);