huh TIL... Thanks, I now see that there's no problem with the type inference.
On Wednesday, 22 December 2021 at 4:48:02 pm UTC+11 Ian Lance Taylor wrote: > On Tue, Dec 21, 2021 at 9:42 PM Corin Lawson <corin....@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/602dbfe3-18e2-4cd2-8cf3-72204cfc4ac1n%40googlegroups.com.
