Make clear in docs you may need to `unthunk` the return from a pullback

JuliaDiff / ChainRulesCore.jl

AD-backend agnostic system defining custom forward and reverse mode rules. This is the light weight core to allow you to define rules for your functions in your packages, without depending on any particular AD system.

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Make clear in docs you may need to `unthunk` the return from a pullback #154

Open nickrobinson251 opened 4 years ago

nickrobinson251 commented 4 years ago

e.g. "things should be unthunked before being passed to pullbacks"

We show this in the "using ChainRules directly" example [edit: not anymore]
And it makes sense once you think about it
But i'd never thought about it til it was pointed out (https://github.com/JuliaDiff/ChainRules.jl/pull/175#discussion_r416521562)... so maybe the docs should explicitly point it out (afaict they don't).

nickrobinson251 commented 4 years ago

As mentioned in https://github.com/JuliaDiff/ChainRules.jl/issues/247 the more general "issue" is Thunks can be returned from a pullback and we should comment on that (and the subsequent need to unthunk)