func (t *Named) TypeParams() *TypeParamList { return t.resolve().tparams }

// SetTypeParams sets the type parameters of the named type t.
// t must not have type arguments.
func (t *Named) SetTypeParams(tparams []*TypeParam) {
	assert(t.inst == nil)
	t.resolve().tparams = bindTParams(tparams)
}

// TypeArgs returns the type arguments used to instantiate the named type t.

}

func (w *typeWriter) signature(sig *Signature) {
	if sig.TypeParams().Len() != 0 {
		if w.ctxt != nil {
			assert(w.tparams == nil)
			w.tparams = sig.TypeParams()
			defer func() {
				w.tparams = nil
			}()
		}
		w.tParamList(sig.TypeParams().list())
	}

	w.tuple(sig.params, sig.variadic)

	n := sig.results.Len()
	if n == 0 {
		// no result
		return
	}

	w.byte(' ')

				// hasher.
				ptrMap:     h.ptrMap,
				sigTParams: tparams,
			}
		}

		for i := 0; i < tparams.Len(); i++ {
			tparam := tparams.At(i)
			hash += 7 * h.Hash(tparam.Constraint())
		}

		return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())

	case *types.Union:
		return h.hashUnion(t)

	case *types.Interface:

func (u *unifier) String() string {
	// sort type parameters for reproducible strings
	tparams := make(typeParamsById, len(u.handles))
	i := 0
	for tpar := range u.handles {
		tparams[i] = tpar
		i++
	}
	sort.Sort(tparams)

	var buf bytes.Buffer
	w := newTypeWriter(&buf, nil)
	w.byte('[')
	for i, x := range tparams {
		if i > 0 {
			w.string(", ")
		}
		w.typ(x)
		w.string(": ")

func (u *unifier) String() string {
	// sort type parameters for reproducible strings
	tparams := make(typeParamsById, len(u.handles))
	i := 0
	for tpar := range u.handles {
		tparams[i] = tpar
		i++
	}
	sort.Sort(tparams)

	var buf bytes.Buffer
	w := newTypeWriter(&buf, nil)
	w.byte('[')
	for i, x := range tparams {
		if i > 0 {
			w.string(", ")
		}
		w.typ(x)
		w.string(": ")

		a.apply(n, "Elt", nil, n.Elt)

	case *ast.StructType:
		a.apply(n, "Fields", nil, n.Fields)

	case *ast.FuncType:
		if tparams := n.TypeParams; tparams != nil {
			a.apply(n, "TypeParams", nil, tparams)
		}
		a.apply(n, "Params", nil, n.Params)
		a.apply(n, "Results", nil, n.Results)

	case *ast.InterfaceType:
		a.apply(n, "Methods", nil, n.Methods)

	case *ast.MapType:

}

func (w *typeWriter) signature(sig *Signature) {
	if sig.TypeParams().Len() != 0 {
		if w.ctxt != nil {
			assert(w.tparams == nil)
			w.tparams = sig.TypeParams()
			defer func() {
				w.tparams = nil
			}()
		}
		w.tParamList(sig.TypeParams().list())
	}

	w.tuple(sig.params, sig.variadic)

	n := sig.results.Len()
	if n == 0 {
		// no result
		return
	}

	w.byte(' ')

		f.walk(&n.Len, ctxExpr, visit)
		f.walk(&n.Elt, ctxType, visit)
	case *ast.StructType:
		f.walk(n.Fields, ctxField, visit)
	case *ast.FuncType:
		if tparams := funcTypeTypeParams(n); tparams != nil {
			f.walk(tparams, ctxParam, visit)
		}
		f.walk(n.Params, ctxParam, visit)
		if n.Results != nil {
			f.walk(n.Results, ctxParam, visit)
		}
	case *ast.InterfaceType:
		f.walk(n.Methods, ctxField, visit)

		recv := t.recv

		params := subst.tuple(t.params)
		results := subst.tuple(t.results)
		if params != t.params || results != t.results {
			return &Signature{
				rparams: t.rparams,
				// TODO(gri) why can't we nil out tparams here, rather than in instantiate?
				tparams: t.tparams,
				// instantiated signatures have a nil scope
				recv:     recv,
				params:   params,
				results:  results,

			}
		}

		tparam := pkg.formatTypeParams(n.TypeParams, depth)
		param := joinStrings(params)
		if len(results) == 0 {
			return fmt.Sprintf("func%s(%s)", tparam, param)
		}
		result := joinStrings(results)
		if !needParens {
			return fmt.Sprintf("func%s(%s) %s", tparam, param, result)
		}
		return fmt.Sprintf("func%s(%s) (%s)", tparam, param, result)

	case *ast.StructType: