The Go spec says:
A partial type argument list specifies a prefix of the full list of type
arguments, leaving the remaining arguments to be inferred. Loosely
speaking, type arguments may be omitted from "right to left" (Source
<https://tip.golang.org/ref/spec#Instantiations>).
This means it is legal:
*type E[T1, T2 any] struct{ … }*
*T[]*
*T[int]*
*T[int, int]*
And this is not legal:
*T[_, int]*
*T[, int]*
I'm wondering which is the reasoning behind this restriction. Is it a
limitation of the current implementation? Is it a design limitation? Is it
just that nobody asked for it?
I'm posting this question because I've seen several colleagues (and myself)
trying to use partial type lists which do not follow the "type arguments
can be omitted from right to left" rule, and the first impression when you
see the compiler yielding "syntax error: unexpected comma, expecting
expression" is at least confusing.
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