If that's correct, then is this what you need? https://go.dev/play/p/_e-Uipgo5OQ It seems quite straightforward so I think I'm missing some context, but this can be a start.
I made an example of what Im trying to do. One thing I didnt specify is the function used is a receiver function. For some reason this means the type had to be instantiated on the receiver itself Spotter in this case. https://goplay.tools/snippet/Vj7uVMi0mWn Basically have two different types that implement an interface, pass them into a receiver function in a composite type (array,slice). Part of the issue is that you cant have the receiver function without defining instantiating the type on the receiver Spotter in this case.
https://go.googlesource.com/proposal/+/refs/heads/master/des...
I believe the most simple fix would be to have a separate function which is generic that takes in the struct along with the slice of T with the constraints that apply to it.