// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package typeutil defines various utilities for types, such as Map,
// a mapping from types.Type to interface{} values.
package typeutil // import "golang.org/x/tools/go/types/typeutil"
import (
"bytes"
"fmt"
"go/types"
"reflect"
)
// Map is a hash-table-based mapping from types (types.Type) to
// arbitrary interface{} values. The concrete types that implement
// the Type interface are pointers. Since they are not canonicalized,
// == cannot be used to check for equivalence, and thus we cannot
// simply use a Go map.
//
// Just as with map[K]V, a nil *Map is a valid empty map.
//
// Not thread-safe.
//
type Map struct {
hasher Hasher // shared by many Maps
table map[uint32][]entry // maps hash to bucket; entry.key==nil means unused
length int // number of map entries
}
// entry is an entry (key/value association) in a hash bucket.
type entry struct {
key types.Type
value interface{}
}
// SetHasher sets the hasher used by Map.
//
// All Hashers are functionally equivalent but contain internal state
// used to cache the results of hashing previously seen types.
//
// A single Hasher created by MakeHasher() may be shared among many
// Maps. This is recommended if the instances have many keys in
// common, as it will amortize the cost of hash computation.
//
// A Hasher may grow without bound as new types are seen. Even when a
// type is deleted from the map, the Hasher never shrinks, since other
// types in the map may reference the deleted type indirectly.
//
// Hashers are not thread-safe, and read-only operations such as
// Map.Lookup require updates to the hasher, so a full Mutex lock (not a
// read-lock) is require around all Map operations if a shared
// hasher is accessed from multiple threads.
//
// If SetHasher is not called, the Map will create a private hasher at
// the first call to Insert.
//
func (m *Map) SetHasher(hasher Hasher) {
m.hasher = hasher
}
// Delete removes the entry with the given key, if any.
// It returns true if the entry was found.
//
func (m *Map) Delete(key types.Type) bool {
if m != nil && m.table != nil {
hash := m.hasher.Hash(key)
bucket := m.table[hash]
for i, e := range bucket {
if e.key != nil && types.Identical(key, e.key) {
// We can't compact the bucket as it
// would disturb iterators.
bucket[i] = entry{}
m.length--
return true
}
}
}
return false
}
// At returns the map entry for the given key.
// The result is nil if the entry is not present.
//
func (m *Map) At(key types.Type) interface{} {
if m != nil && m.table != nil {
for _, e := range m.table[m.hasher.Hash(key)] {
if e.key != nil && types.Identical(key, e.key) {
return e.value
}
}
}
return nil
}
// Set sets the map entry for key to val,
// and returns the previous entry, if any.
func (m *Map) Set(key types.Type, value interface{}) (prev interface{}) {
if m.table != nil {
hash := m.hasher.Hash(key)
bucket := m.table[hash]
var hole *entry
for i, e := range bucket {
if e.key == nil {
hole = &bucket[i]
} else if types.Identical(key, e.key) {
prev = e.value
bucket[i].value = value
return
}
}
if hole != nil {
*hole = entry{key, value} // overwrite deleted entry
} else {
m.table[hash] = append(bucket, entry{key, value})
}
} else {
if m.hasher.memo == nil {
m.hasher = MakeHasher()
}
hash := m.hasher.Hash(key)
m.table = map[uint32][]entry{hash: {entry{key, value}}}
}
m.length++
return
}
// Len returns the number of map entries.
func (m *Map) Len() int {
if m != nil {
return m.length
}
return 0
}
// Iterate calls function f on each entry in the map in unspecified order.
//
// If f should mutate the map, Iterate provides the same guarantees as
// Go maps: if f deletes a map entry that Iterate has not yet reached,
// f will not be invoked for it, but if f inserts a map entry that
// Iterate has not yet reached, whether or not f will be invoked for
// it is unspecified.
//
func (m *Map) Iterate(f func(key types.Type, value interface{})) {
if m != nil {
for _, bucket := range m.table {
for _, e := range bucket {
if e.key != nil {
f(e.key, e.value)
}
}
}
}
}
// Keys returns a new slice containing the set of map keys.
// The order is unspecified.
func (m *Map) Keys() []types.Type {
keys := make([]types.Type, 0, m.Len())
m.Iterate(func(key types.Type, _ interface{}) {
keys = append(keys, key)
})
return keys
}
func (m *Map) toString(values bool) string {
if m == nil {
return "{}"
}
var buf bytes.Buffer
fmt.Fprint(&buf, "{")
sep := ""
m.Iterate(func(key types.Type, value interface{}) {
fmt.Fprint(&buf, sep)
sep = ", "
fmt.Fprint(&buf, key)
if values {
fmt.Fprintf(&buf, ": %q", value)
}
})
fmt.Fprint(&buf, "}")
return buf.String()
}
// String returns a string representation of the map's entries.
// Values are printed using fmt.Sprintf("%v", v).
// Order is unspecified.
//
func (m *Map) String() string {
return m.toString(true)
}
// KeysString returns a string representation of the map's key set.
// Order is unspecified.
//
func (m *Map) KeysString() string {
return m.toString(false)
}
////////////////////////////////////////////////////////////////////////
// Hasher
// A Hasher maps each type to its hash value.
// For efficiency, a hasher uses memoization; thus its memory
// footprint grows monotonically over time.
// Hashers are not thread-safe.
// Hashers have reference semantics.
// Call MakeHasher to create a Hasher.
type Hasher struct {
memo map[types.Type]uint32
}
// MakeHasher returns a new Hasher instance.
func MakeHasher() Hasher {
return Hasher{make(map[types.Type]uint32)}
}
// Hash computes a hash value for the given type t such that
// Identical(t, t') => Hash(t) == Hash(t').
func (h Hasher) Hash(t types.Type) uint32 {
hash, ok := h.memo[t]
if !ok {
hash = h.hashFor(t)
h.memo[t] = hash
}
return hash
}
// hashString computes the Fowler–Noll–Vo hash of s.
func hashString(s string) uint32 {
var h uint32
for i := 0; i < len(s); i++ {
h ^= uint32(s[i])
h *= 16777619
}
return h
}
// hashFor computes the hash of t.
func (h Hasher) hashFor(t types.Type) uint32 {
// See Identical for rationale.
switch t := t.(type) {
case *types.Basic:
return uint32(t.Kind())
case *types.Array:
return 9043 + 2*uint32(t.Len()) + 3*h.Hash(t.Elem())
case *types.Slice:
return 9049 + 2*h.Hash(t.Elem())
case *types.Struct:
var hash uint32 = 9059
for i, n := 0, t.NumFields(); i < n; i++ {
f := t.Field(i)
if f.Anonymous() {
hash += 8861
}
hash += hashString(t.Tag(i))
hash += hashString(f.Name()) // (ignore f.Pkg)
hash += h.Hash(f.Type())
}
return hash
case *types.Pointer:
return 9067 + 2*h.Hash(t.Elem())
case *types.Signature:
var hash uint32 = 9091
if t.Variadic() {
hash *= 8863
}
return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())
case *types.Interface:
var hash uint32 = 9103
for i, n := 0, t.NumMethods(); i < n; i++ {
// See go/types.identicalMethods for rationale.
// Method order is not significant.
// Ignore m.Pkg().
m := t.Method(i)
hash += 3*hashString(m.Name()) + 5*h.Hash(m.Type())
}
return hash
case *types.Map:
return 9109 + 2*h.Hash(t.Key()) + 3*h.Hash(t.Elem())
case *types.Chan:
return 9127 + 2*uint32(t.Dir()) + 3*h.Hash(t.Elem())
case *types.Named:
// Not safe with a copying GC; objects may move.
return uint32(reflect.ValueOf(t.Obj()).Pointer())
case *types.Tuple:
return h.hashTuple(t)
}
panic(t)
}
func (h Hasher) hashTuple(tuple *types.Tuple) uint32 {
// See go/types.identicalTypes for rationale.
n := tuple.Len()
var hash uint32 = 9137 + 2*uint32(n)
for i := 0; i < n; i++ {
hash += 3 * h.Hash(tuple.At(i).Type())
}
return hash
}
