// IntuitiveMethodSet returns the intuitive method set of a type, T.
//
// The result contains MethodSet(T) and additionally, if T is a
// concrete type, methods belonging to *T if there is no identically
// named method on T itself. This corresponds to user intuition about
// method sets; this function is intended only for user interfaces.
//
// The order of the result is as for types.MethodSet(T).
//
func IntuitiveMethodSet(T types.Type, msets *types.MethodSetCache) []*types.Selection {
var result []*types.Selection
mset := msets.MethodSet(T)
if _, ok := T.Underlying().(*types.Interface); ok {
for i, n := 0, mset.Len(); i < n; i++ {
result = append(result, mset.At(i))
}
} else {
pmset := msets.MethodSet(types.NewPointer(T))
for i, n := 0, pmset.Len(); i < n; i++ {
meth := pmset.At(i)
if m := mset.Lookup(meth.Obj().Pkg(), meth.Obj().Name()); m != nil {
meth = m
}
result = append(result, meth)
}
}
return result
}
// computeImplements computes the "implements" relation over all pairs
// of named types in allNamed.
func computeImplements(cache *types.MethodSetCache, allNamed []*types.Named) map[*types.Named]implementsFacts {
// Information about a single type's method set.
type msetInfo struct {
typ types.Type
mset *types.MethodSet
mask1, mask2 uint64
}
initMsetInfo := func(info *msetInfo, typ types.Type) {
info.typ = typ
info.mset = cache.MethodSet(typ)
for i := 0; i < info.mset.Len(); i++ {
name := info.mset.At(i).Obj().Name()
info.mask1 |= 1 << methodBit(name[0])
info.mask2 |= 1 << methodBit(name[len(name)-1])
}
}
// satisfies(T, U) reports whether type T satisfies type U.
// U must be an interface.
//
// Since there are thousands of types (and thus millions of
// pairs of types) and types.Assignable(T, U) is relatively
// expensive, we compute assignability directly from the
// method sets. (At least one of T and U must be an
// interface.)
//
// We use a trick (thanks gri!) related to a Bloom filter to
// quickly reject most tests, which are false. For each
// method set, we precompute a mask, a set of bits, one per
// distinct initial byte of each method name. Thus the mask
// for io.ReadWriter would be {'R','W'}. AssignableTo(T, U)
// cannot be true unless mask(T)&mask(U)==mask(U).
//
// As with a Bloom filter, we can improve precision by testing
// additional hashes, e.g. using the last letter of each
// method name, so long as the subset mask property holds.
//
// When analyzing the standard library, there are about 1e6
// calls to satisfies(), of which 0.6% return true. With a
// 1-hash filter, 95% of calls avoid the expensive check; with
// a 2-hash filter, this grows to 98.2%.
satisfies := func(T, U *msetInfo) bool {
return T.mask1&U.mask1 == U.mask1 &&
T.mask2&U.mask2 == U.mask2 &&
containsAllIdsOf(T.mset, U.mset)
}
// Information about a named type N, and perhaps also *N.
type namedInfo struct {
isInterface bool
base msetInfo // N
ptr msetInfo // *N, iff N !isInterface
}
var infos []namedInfo
// Precompute the method sets and their masks.
for _, N := range allNamed {
var info namedInfo
initMsetInfo(&info.base, N)
_, info.isInterface = N.Underlying().(*types.Interface)
if !info.isInterface {
initMsetInfo(&info.ptr, types.NewPointer(N))
}
if info.base.mask1|info.ptr.mask1 == 0 {
continue // neither N nor *N has methods
}
infos = append(infos, info)
}
facts := make(map[*types.Named]implementsFacts)
// Test all pairs of distinct named types (T, U).
// TODO(adonovan): opt: compute (U, T) at the same time.
for t := range infos {
T := &infos[t]
var to, from, fromPtr []types.Type
for u := range infos {
if t == u {
continue
}
U := &infos[u]
switch {
case T.isInterface && U.isInterface:
if satisfies(&U.base, &T.base) {
to = append(to, U.base.typ)
}
if satisfies(&T.base, &U.base) {
from = append(from, U.base.typ)
}
case T.isInterface: // U concrete
if satisfies(&U.base, &T.base) {
to = append(to, U.base.typ)
} else if satisfies(&U.ptr, &T.base) {
to = append(to, U.ptr.typ)
}
case U.isInterface: // T concrete
if satisfies(&T.base, &U.base) {
from = append(from, U.base.typ)
} else if satisfies(&T.ptr, &U.base) {
fromPtr = append(fromPtr, U.base.typ)
}
}
}
// Sort types (arbitrarily) to avoid nondeterminism.
sort.Sort(typesByString(to))
sort.Sort(typesByString(from))
sort.Sort(typesByString(fromPtr))
facts[T.base.typ.(*types.Named)] = implementsFacts{to, from, fromPtr}
}
return facts
}