444 lines
12 KiB
Go
444 lines
12 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 // import "golang.org/x/tools/go/types/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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"golang.org/x/tools/internal/typeparams"
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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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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 && types.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 && types.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 types.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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// ptrMap records pointer identity.
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ptrMap map[interface{}]uint32
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// sigTParams holds type parameters from the signature being hashed.
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// Signatures are considered identical modulo renaming of type parameters, so
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// within the scope of a signature type the identity of the signature's type
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// parameters is just their index.
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//
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// Since the language does not currently support referring to uninstantiated
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// generic types or functions, and instantiated signatures do not have type
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// parameter lists, we should never encounter a second non-empty type
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// parameter list when hashing a generic signature.
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sigTParams *typeparams.TypeParamList
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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{
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memo: make(map[types.Type]uint32),
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ptrMap: make(map[interface{}]uint32),
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sigTParams: nil,
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}
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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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// Use a separate hasher for types inside of the signature, where type
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// parameter identity is modified to be (index, constraint). We must use a
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// new memo for this hasher as type identity may be affected by this
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// masking. For example, in func[T any](*T), the identity of *T depends on
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// whether we are mapping the argument in isolation, or recursively as part
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// of hashing the signature.
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//
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// We should never encounter a generic signature while hashing another
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// generic signature, but defensively set sigTParams only if h.mask is
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// unset.
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tparams := typeparams.ForSignature(t)
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if h.sigTParams == nil && tparams.Len() != 0 {
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h = Hasher{
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// There may be something more efficient than discarding the existing
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// memo, but it would require detecting whether types are 'tainted' by
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// references to type parameters.
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memo: make(map[types.Type]uint32),
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// Re-using ptrMap ensures that pointer identity is preserved in this
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// hasher.
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ptrMap: h.ptrMap,
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sigTParams: tparams,
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}
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}
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for i := 0; i < tparams.Len(); i++ {
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tparam := tparams.At(i)
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hash += 7 * h.Hash(tparam.Constraint())
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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 *typeparams.Union:
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return h.hashUnion(t)
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case *types.Interface:
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// Interfaces are identical if they have the same set of methods, with
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// identical names and types, and they have the same set of type
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// restrictions. See go/types.identical for more details.
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var hash uint32 = 9103
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// Hash methods.
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for i, n := 0, t.NumMethods(); i < n; i++ {
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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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// Hash type restrictions.
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terms, err := typeparams.InterfaceTermSet(t)
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// if err != nil t has invalid type restrictions.
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if err == nil {
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hash += h.hashTermSet(terms)
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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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hash := h.hashPtr(t.Obj())
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targs := typeparams.NamedTypeArgs(t)
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for i := 0; i < targs.Len(); i++ {
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targ := targs.At(i)
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hash += 2 * h.Hash(targ)
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}
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return hash
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case *typeparams.TypeParam:
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return h.hashTypeParam(t)
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case *types.Tuple:
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return h.hashTuple(t)
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}
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panic(fmt.Sprintf("%T: %v", t, 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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hash := 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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func (h Hasher) hashUnion(t *typeparams.Union) uint32 {
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// Hash type restrictions.
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terms, err := typeparams.UnionTermSet(t)
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// if err != nil t has invalid type restrictions. Fall back on a non-zero
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// hash.
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if err != nil {
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return 9151
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}
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return h.hashTermSet(terms)
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}
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func (h Hasher) hashTermSet(terms []*typeparams.Term) uint32 {
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hash := 9157 + 2*uint32(len(terms))
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for _, term := range terms {
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// term order is not significant.
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termHash := h.Hash(term.Type())
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if term.Tilde() {
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termHash *= 9161
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}
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hash += 3 * termHash
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}
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return hash
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}
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// hashTypeParam returns a hash of the type parameter t, with a hash value
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// depending on whether t is contained in h.sigTParams.
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//
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// If h.sigTParams is set and contains t, then we are in the process of hashing
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// a signature, and the hash value of t must depend only on t's index and
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// constraint: signatures are considered identical modulo type parameter
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// renaming. To avoid infinite recursion, we only hash the type parameter
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// index, and rely on types.Identical to handle signatures where constraints
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// are not identical.
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//
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// Otherwise the hash of t depends only on t's pointer identity.
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func (h Hasher) hashTypeParam(t *typeparams.TypeParam) uint32 {
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if h.sigTParams != nil {
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i := t.Index()
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if i >= 0 && i < h.sigTParams.Len() && t == h.sigTParams.At(i) {
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return 9173 + 3*uint32(i)
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}
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}
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return h.hashPtr(t.Obj())
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}
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// hashPtr hashes the pointer identity of ptr. It uses h.ptrMap to ensure that
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// pointers values are not dependent on the GC.
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func (h Hasher) hashPtr(ptr interface{}) uint32 {
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if hash, ok := h.ptrMap[ptr]; ok {
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return hash
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}
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hash := uint32(reflect.ValueOf(ptr).Pointer())
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h.ptrMap[ptr] = hash
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return hash
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}
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