know the location of every pointer to Go memory. Because of this,
there are restrictions on passing pointers between Go and C.

In this section the term Go pointer means a pointer to memory
allocated by Go (such as by using the & operator or calling the
predefined new function) and the term C pointer means a pointer to
memory allocated by C (such as by a call to C.malloc). Whether a
pointer is a Go pointer or a C pointer is a dynamic property

pkg go/types, method (*Signature) RecvTypeParams() *TypeParamList
pkg go/types, method (*Signature) TypeParams() *TypeParamList
pkg go/types, method (*Term) String() string
pkg go/types, method (*Term) Tilde() bool
pkg go/types, method (*Term) Type() Type
pkg go/types, method (*TypeList) At(int) Type
pkg go/types, method (*TypeList) Len() int
pkg go/types, method (*TypeParam) Constraint() Type

// expr = term | term ('+' | '-' | '|' | '^') term.
func (p *Parser) expr() uint64 {
	value := p.term()
	for {
		switch p.peek() {
		case '+':
			p.next()
			value += p.term()
		case '-':
			p.next()
			value -= p.term()
		case '|':
			p.next()
			value |= p.term()
		case '^':
			p.next()
			value ^= p.term()
		default:
			return value
		}

		case *types.Union:
			var buf bytes.Buffer
			nu := emb.Len()
			for i := 0; i < nu; i++ {
				if i > 0 {
					buf.WriteString(" | ")
				}
				term := emb.Term(i)
				if term.Tilde() {
					buf.WriteByte('~')
				}
				w.writeType(&buf, term.Type())
			}
			list = append(list, buf.String())
		}
	}
	sort.Strings(list)
	return list
}