github.com/cockroachdb/tools@v0.0.0-20230222021103-a6d27438930d/go/types/typeutil/methodsetcache.go (about)

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // This file implements a cache of method sets.
     6  
     7  package typeutil
     8  
     9  import (
    10  	"go/types"
    11  	"sync"
    12  )
    13  
    14  // A MethodSetCache records the method set of each type T for which
    15  // MethodSet(T) is called so that repeat queries are fast.
    16  // The zero value is a ready-to-use cache instance.
    17  type MethodSetCache struct {
    18  	mu     sync.Mutex
    19  	named  map[*types.Named]struct{ value, pointer *types.MethodSet } // method sets for named N and *N
    20  	others map[types.Type]*types.MethodSet                            // all other types
    21  }
    22  
    23  // MethodSet returns the method set of type T.  It is thread-safe.
    24  //
    25  // If cache is nil, this function is equivalent to types.NewMethodSet(T).
    26  // Utility functions can thus expose an optional *MethodSetCache
    27  // parameter to clients that care about performance.
    28  func (cache *MethodSetCache) MethodSet(T types.Type) *types.MethodSet {
    29  	if cache == nil {
    30  		return types.NewMethodSet(T)
    31  	}
    32  	cache.mu.Lock()
    33  	defer cache.mu.Unlock()
    34  
    35  	switch T := T.(type) {
    36  	case *types.Named:
    37  		return cache.lookupNamed(T).value
    38  
    39  	case *types.Pointer:
    40  		if N, ok := T.Elem().(*types.Named); ok {
    41  			return cache.lookupNamed(N).pointer
    42  		}
    43  	}
    44  
    45  	// all other types
    46  	// (The map uses pointer equivalence, not type identity.)
    47  	mset := cache.others[T]
    48  	if mset == nil {
    49  		mset = types.NewMethodSet(T)
    50  		if cache.others == nil {
    51  			cache.others = make(map[types.Type]*types.MethodSet)
    52  		}
    53  		cache.others[T] = mset
    54  	}
    55  	return mset
    56  }
    57  
    58  func (cache *MethodSetCache) lookupNamed(named *types.Named) struct{ value, pointer *types.MethodSet } {
    59  	if cache.named == nil {
    60  		cache.named = make(map[*types.Named]struct{ value, pointer *types.MethodSet })
    61  	}
    62  	// Avoid recomputing mset(*T) for each distinct Pointer
    63  	// instance whose underlying type is a named type.
    64  	msets, ok := cache.named[named]
    65  	if !ok {
    66  		msets.value = types.NewMethodSet(named)
    67  		msets.pointer = types.NewMethodSet(types.NewPointer(named))
    68  		cache.named[named] = msets
    69  	}
    70  	return msets
    71  }