去正确的行为，还是编译器错误？

Question

package main

type Key struct {
    stuff1 string
    stuff2 []string
}

type Val struct {
}

type MyMap struct {
    map1 map[Key]*Val // compiles fine!
}

func main() {
    var map2 map[Key]*Val // "invalid map key type Key"
}

Is this the correct behaviour, or a bug in go compiler?

I am using go-1.1 on Linux x64.

Answer 1

The compiler is right. From the specs: Map Types:

The comparison operators == and != must be fully defined for operands of the key type; thus the key type must not be a function, map, or slice.

This restriction applies transitively if the key type is a struct to all of the struct fields, they must obey the above quoted rule as well, which

stuff2 []string

does not.

EDIT:

What concerns map1 not being flagged, that probably is a bug, perhaps caused by MyMap never being referenced and thus it's type checking was probably skipped.