Preventing the application of the same Layer to the Operator fo multiple times

[ClSlaid]

As the completion of layers support in v0.13, users can simply call layer(<Layer>) on operators, to enable logging, metrics, tracing and retry features.

However, current implementation of layers cannot prevent users from duplicately wrapping operators with a same layer, which could lead to redundant logging or even wrong metrics.

[Xuanwo]

I don't know whether we should take care of this - -

[Xuanwo]

I don't know whether we should take care of this - -

Sorry @ClSlaid, I'm wrong. It's very easily for application to call layer on the same layer for many times...

Do you have any good ideas for that?

[ClSlaid]

We can add an new API like layer_applied(&self, layer: LayerKind) -> bool in Accessor trait.

LayerKind is an enum coordinate with actual layers like TracingLayer, before applying the layer to inner accessors, the implemented Layer::layer function should first check with layer_applied, and return the accessor to wrap directly if did already apply.

[Xuanwo]

We can add an new API like layer_applied(&self, layer: LayerKind) -> bool in Accessor trait.

We should not touch Accessor.

[Xuanwo]

Not actionable. Let's move to discussion.