# Error when mixing a yet-to-be-bound parametric type

#1

Error message:

“Persistable reference field is of parametric type. All parameters for reference fields must be bound.”

Example:
Type ABC is parametric
`entity type XYZ mixes TimedValueHistory<ABC>`

How should the type be declared to avoid this error?

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#3

Since both `TimedValueHistory` and `ABC` are parametric types, you must provide bindings for both when mixing them in type `XYZ`. I think this should work:

``````entity type XYZ mixes TimedValueHistory<ABC<SomeNonParametricType>>
``````

where `SomeNonParametricType` is the binding for `ABC`, and `ABC<SomeNonParametricType>` is the binding for `TimedValueHistory`

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