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