fabric.refs

Module nu.context.fabric.refs.

FabricRef: a Ref into a Context binding.

Every ctx-bound thing is a Fabric (the empty marker Protocol). A FabricRef names one by its resolved address (the fabric type). The read is the dual role: self-yield the bound fabric (EMPTY when unbound). Fabrics are bound on the Context, not written through a Ref, so FabricRef is read-only as a value.

FabricRef

A Ref into a Context binding, keyed by the fabric type it resolves to.

FabricRef(address=None)

Path nu.context.FabricRef. Kind Ref, sort ref, cardinality scalar.

The sole child is the address, and it resolves to a type rather than to a key: the read looks that type up on the Context and self-yields whatever instance is bound there. Nothing is ever written through this Ref - instances arrive on the Context from a Provide bracket, so the value side of a FabricRef is read-only.

Each concrete fabric gets its own subclass carrying the type it names in the fabric class attribute, which is what the address falls back to when none is passed:

class Solana(FabricRef):
    fabric = SolanaClient

Solana() then resolves SolanaClient from the Context. A bare FabricRef(SolanaClient) still works for the untyped, one-off read.

Notes

• This base reads the untagged binding only. Context resolution falls back from more tags to fewer, never the other way, so an instance bound under Provide(..., tag="a") is not reachable here. A subclass that wants tags stores them itself and forwards them to ctx.get (see nustd.cluster.refs.RayServiceRef).
• A binding holding EMPTY and no binding at all read the same, so use .exists() when the difference matters.
• The fabric axis is for the long-lived, typed things - storage handles, cluster handles, clients. Short-lived scratch values live on the attrs axis behind AttrRef.

Examples

class Counter:
    def __init__(self, start=0):
        self.n = start
nu.run(nu.Provide(Counter, {"start": 5}, nu.FabricRef(Counter).exists()))[0]

True

nu.run(nu.FabricRef(Counter).exists())[0]

False

Methods

.exists()

A Query yielding whether this Ref's fabric type is bound on the Context.

Builds FabricExists.

Notes

• The plain read cannot answer this: an unbound type yields EMPTY and so does a type bound to EMPTY.

Undocumented: example.