Techniques herein processes type assignments for a generic class to generate a concrete class. In an embodiment, a computer analyzes a client class to detect a dependency on a generic class having type parameters. The client class contains a specialization context that specifies type assignments for the type parameters. Each type parameter is associated with particular type entries in the generic class that identify an erasure type to use in case the type parameter is erased. The computer generates instantiation metadata for the generic class including, for each type entry, performing the following. In response to determining that the specialization context specifies binding a particular type to the type parameter associated with the type entry, the computer generates an entry for the instantiation metadata that identifies the particular type. Otherwise, the computer generates an entry for the instantiation metadata that identifies an erasure type of the type entry.