On Tue, Dec 21, 2021 at 9:42 PM Corin Lawson <corin.law...@gmail.com> wrote: > > I'm new here, but write Go on a daily basis for fun and profit. The other > day I wrote a giant type switch that was intended to organise a bag of > various things into various bags each containing things of a single concrete > type. For example: https://go.dev/play/p/fqYXEP2YG_9 (Note that the real > world code is consuming structs that have been generated by go-swagger). The > slices in the map returned by `partitionByActionRequestType` are more > convenient (after a type assertion) to work with, but in the example we are > simply printing them. Say, what you will about this code; my question is > concerned with how to use generics to simplify the code (assuming generics is > appropriate in this case). > > My first attempt reduced a lot of the copy'n'paste: > https://go.dev/play/p/XyTL0eqtwiR?v=gotip. It introduces a generic function > that performs the slice construction and append of each branch, thereby > reducing each branch into one line. This seems like an improvement to me, > but observe how the body of each branch is identical > (character-for-character). > > My next attempt involved collapsing branches: > https://go.dev/play/p/t9E7jW6-xtz?v=gotip. In this case the type inference > did something unexpected, and we encounter the following error: > > ``` > panic: interface conversion: interface {} is []main.ActionRequest, not > []*main.Build > ``` > > The inferred type is more generic than desired; i.e. the type that is known > prior to the type switch (i.e. the type of `next`) is the type that is > inferred not the type that the type switch has determined (i.e. the type of > `actionRequest`). > > Am I wrong to expect this behaviour from the type inference?
When you write a case like `case *Build, *Test, *Run:` the type in the case body does not change. The type only changes if there is just a single type in the case. So the type of actionRequest is ActionRequest, which is why you get those results. Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcVHmzZFP%3DQnVfnZo0rfoAgiMuT9ftDVXSr68xb%2ByFPn_Q%40mail.gmail.com.
