Storages and delegation

[dmdashenkov]

Currently, it is not easy to create an implementation of, e.g. ProjectionStorage, which would delegate its operations to another instance of ProjectionStorage.

The problem is in protected methods.

package org.example;

// ...

class MyProjectionStorage<I> extends ProjectionStorage<I> {

    private final ProjectionStorage<I> delegate;

    @Override
    protected Optional<EntityRecord> readRecord(I id) {
        return delagate.readRecord(id); 
        //              ^
        // Compiler error here, cannot access protected method `readRecord`
        //  outside the Spine package.
    }
    
    // ...
}

There are a few methods in ProjectionStorage and other case-specific storages such as readRecord, which are declared protected making it impossible to delegate them.

[dmdashenkov]

Currently, I offer to resolve this when we re-design out storages to fit all purposes with just one MessageStorage.

[dmdashenkov]

@armiol, FYI. @nick-dolgiy, please feel free to add further details.