Golang：键入断言错误问题(Golang: Type Assertion Error issue)

我被代码片段下面的类型断言相关错误所困扰。 我不确定我错过了什么。 我在以下地方做类型断言itr = itr。（* DbIterator）.Iterator and key：= itr.Key（）。（* Key）.Slice and value：= itr.Value（）。（* Value）。片。 我想知道是否有更好的方法来做到这一点，没有代码库中的类型断言或更好的设计模式来处理这种情况。 代码段是更大代码库的一部分。 我已经为这个问题提取了最相关的部分。 在这方面的任何帮助非常感谢。

package rocksdb import ( "github.com/tecbot/gorocksdb" ) func (s *RocksDB) GetCFIterator(cfHandler *gorocksdb.ColumnFamilyHandle) db.Iterator { opt := gorocksdb.NewDefaultReadOptions() opt.SetFillCache(true) defer opt.Destroy() return &DbIterator{s.DB.NewIteratorCF(opt, cfHandler)} } type DbIterator struct { *gorocksdb.Iterator } type Key struct { *gorocksdb.Slice } type Value struct { *gorocksdb.Slice } func (iterator *DbIterator) Key() db.Keyer { return &Key{iterator.Iterator.Key()} } func (iterator *DbIterator) Value() db.Valuer { return &Value{iterator.Iterator.Value()} } type RocksDB struct { DB *gorocksdb.DB }

我有一个interator接口

package db import ( "bytes" "testing" ) type Iterator interface { Valid() bool Next() Close() SeekToFirst() SeekToLast() Seek(key []byte) Key() Keyer Value() Valuer } type Keyer interface { } type Valuer interface { } func testIterator(t *testing.T, itr db.Iterator, expectedValues map[string][]byte) { itrResults := make(map[string][]byte) itr = itr.(*DbIterator).Iterator //Line 270 which the error throws itr.SeekToFirst() for ; itr.Valid(); itr.Next() { key := itr.Key().(*Key).Slice value := itr.Value().(*Value).Slice k := makeCopy(key.Data()) v := makeCopy(value.Data()) itrResults[string(k)] = v } if len(itrResults) != len(expectedValues) { t.Fatalf("Expected [%d] results from iterator, found [%d]", len(expectedValues), len(itrResults)) } for k, v := range expectedValues { if !bytes.Equal(itrResults[k], v) { t.Fatalf("Wrong value for key [%s]. Expected [%s], found [%s]", k, itrResults[k], v) } } }

错误信息

github.com/hyperledger/fabric/core/db/rocksdb core/db/rocksdb/rocksdb_test.go:270: cannot use itr.(*DbIterator).Iterator (type *gorocksdb.Iterator) as type db.Iterator in assignment: *gorocksdb.Iterator does not implement db.Iterator (wrong type for Key method) have Key() *gorocksdb.Slice want Key() db.Keyer

I am getting bitten by the type assertion related error in the below the code snippet. I am not sure what I am missing. I am doing type assertions in the following places itr = itr.(*DbIterator).Iterator and key := itr.Key().(*Key).Slice and value := itr.Value().(*Value).Slice. I am wondering if there is a better way to do this without type assertions everywhere in the code base or better design patterns to handle this kind of scenario. The code snippet is part of a larger code base. I have pulled the most relevant bits for this question. Any help in this regard is much appreciated.

package rocksdb import ( "github.com/tecbot/gorocksdb" ) func (s *RocksDB) GetCFIterator(cfHandler *gorocksdb.ColumnFamilyHandle) db.Iterator { opt := gorocksdb.NewDefaultReadOptions() opt.SetFillCache(true) defer opt.Destroy() return &DbIterator{s.DB.NewIteratorCF(opt, cfHandler)} } type DbIterator struct { *gorocksdb.Iterator } type Key struct { *gorocksdb.Slice } type Value struct { *gorocksdb.Slice } func (iterator *DbIterator) Key() db.Keyer { return &Key{iterator.Iterator.Key()} } func (iterator *DbIterator) Value() db.Valuer { return &Value{iterator.Iterator.Value()} } type RocksDB struct { DB *gorocksdb.DB }

I have an interator interface

package db import ( "bytes" "testing" ) type Iterator interface { Valid() bool Next() Close() SeekToFirst() SeekToLast() Seek(key []byte) Key() Keyer Value() Valuer } type Keyer interface { } type Valuer interface { } func testIterator(t *testing.T, itr db.Iterator, expectedValues map[string][]byte) { itrResults := make(map[string][]byte) itr = itr.(*DbIterator).Iterator //Line 270 which the error throws itr.SeekToFirst() for ; itr.Valid(); itr.Next() { key := itr.Key().(*Key).Slice value := itr.Value().(*Value).Slice k := makeCopy(key.Data()) v := makeCopy(value.Data()) itrResults[string(k)] = v } if len(itrResults) != len(expectedValues) { t.Fatalf("Expected [%d] results from iterator, found [%d]", len(expectedValues), len(itrResults)) } for k, v := range expectedValues { if !bytes.Equal(itrResults[k], v) { t.Fatalf("Wrong value for key [%s]. Expected [%s], found [%s]", k, itrResults[k], v) } } }

Error Message

github.com/hyperledger/fabric/core/db/rocksdb core/db/rocksdb/rocksdb_test.go:270: cannot use itr.(*DbIterator).Iterator (type *gorocksdb.Iterator) as type db.Iterator in assignment: *gorocksdb.Iterator does not implement db.Iterator (wrong type for Key method) have Key() *gorocksdb.Slice want Key() db.Keyer

最满意答案

问题不在于类型断言，你会在那里打破，因为你正在使用的实例没有实现该接口。 话虽如此，你可以通过这样做优雅地处理这个问题;

itr, ok = itr.(*DbIterator) if !ok { //try to recover }

但是，就像我说的那样当你到达那个代码时， itr的类型不是代码所期望的，所以它不会以期望的结果结束，你必须在这里做一些恢复/错误处理才能使它工作更好或弄清楚你是如何在第一时间传递错误类型的。

The problem isn't the type asserts, you're gonna break there regardless because the instance you're working with doesn't implement that interface. That being said you can handle this gracefully by doing;

itr, ok = itr.(*DbIterator) if !ok { //try to recover }

But yeah, like I said when you get to that code the type of itr is not what the code is expecting so it's not going to end with the desired result, you'll have to do some recovery/error handling here to make it work better or figure out how you're getting the wrong type passed down there in the first place.

Golang：键入断言错误问题(Golang: Type Assertion Error issue)

我被代码片段下面的类型断言相关错误所困扰。 我不确定我错过了什么。 我在以下地方做类型断言itr = itr。（* DbIterator）.Iterator and key：= itr.Key（）。（* Key）.Slice and value：= itr.Value（）。（* Value）。片。 我想知道是否有更好的方法来做到这一点，没有代码库中的类型断言或更好的设计模式来处理这种情况。 代码段是更大代码库的一部分。 我已经为这个问题提取了最相关的部分。 在这方面的任何帮助非常感谢。

package rocksdb import ( "github.com/tecbot/gorocksdb" ) func (s *RocksDB) GetCFIterator(cfHandler *gorocksdb.ColumnFamilyHandle) db.Iterator { opt := gorocksdb.NewDefaultReadOptions() opt.SetFillCache(true) defer opt.Destroy() return &DbIterator{s.DB.NewIteratorCF(opt, cfHandler)} } type DbIterator struct { *gorocksdb.Iterator } type Key struct { *gorocksdb.Slice } type Value struct { *gorocksdb.Slice } func (iterator *DbIterator) Key() db.Keyer { return &Key{iterator.Iterator.Key()} } func (iterator *DbIterator) Value() db.Valuer { return &Value{iterator.Iterator.Value()} } type RocksDB struct { DB *gorocksdb.DB }

我有一个interator接口

package db import ( "bytes" "testing" ) type Iterator interface { Valid() bool Next() Close() SeekToFirst() SeekToLast() Seek(key []byte) Key() Keyer Value() Valuer } type Keyer interface { } type Valuer interface { } func testIterator(t *testing.T, itr db.Iterator, expectedValues map[string][]byte) { itrResults := make(map[string][]byte) itr = itr.(*DbIterator).Iterator //Line 270 which the error throws itr.SeekToFirst() for ; itr.Valid(); itr.Next() { key := itr.Key().(*Key).Slice value := itr.Value().(*Value).Slice k := makeCopy(key.Data()) v := makeCopy(value.Data()) itrResults[string(k)] = v } if len(itrResults) != len(expectedValues) { t.Fatalf("Expected [%d] results from iterator, found [%d]", len(expectedValues), len(itrResults)) } for k, v := range expectedValues { if !bytes.Equal(itrResults[k], v) { t.Fatalf("Wrong value for key [%s]. Expected [%s], found [%s]", k, itrResults[k], v) } } }

错误信息

github.com/hyperledger/fabric/core/db/rocksdb core/db/rocksdb/rocksdb_test.go:270: cannot use itr.(*DbIterator).Iterator (type *gorocksdb.Iterator) as type db.Iterator in assignment: *gorocksdb.Iterator does not implement db.Iterator (wrong type for Key method) have Key() *gorocksdb.Slice want Key() db.Keyer

I am getting bitten by the type assertion related error in the below the code snippet. I am not sure what I am missing. I am doing type assertions in the following places itr = itr.(*DbIterator).Iterator and key := itr.Key().(*Key).Slice and value := itr.Value().(*Value).Slice. I am wondering if there is a better way to do this without type assertions everywhere in the code base or better design patterns to handle this kind of scenario. The code snippet is part of a larger code base. I have pulled the most relevant bits for this question. Any help in this regard is much appreciated.

package rocksdb import ( "github.com/tecbot/gorocksdb" ) func (s *RocksDB) GetCFIterator(cfHandler *gorocksdb.ColumnFamilyHandle) db.Iterator { opt := gorocksdb.NewDefaultReadOptions() opt.SetFillCache(true) defer opt.Destroy() return &DbIterator{s.DB.NewIteratorCF(opt, cfHandler)} } type DbIterator struct { *gorocksdb.Iterator } type Key struct { *gorocksdb.Slice } type Value struct { *gorocksdb.Slice } func (iterator *DbIterator) Key() db.Keyer { return &Key{iterator.Iterator.Key()} } func (iterator *DbIterator) Value() db.Valuer { return &Value{iterator.Iterator.Value()} } type RocksDB struct { DB *gorocksdb.DB }

I have an interator interface

package db import ( "bytes" "testing" ) type Iterator interface { Valid() bool Next() Close() SeekToFirst() SeekToLast() Seek(key []byte) Key() Keyer Value() Valuer } type Keyer interface { } type Valuer interface { } func testIterator(t *testing.T, itr db.Iterator, expectedValues map[string][]byte) { itrResults := make(map[string][]byte) itr = itr.(*DbIterator).Iterator //Line 270 which the error throws itr.SeekToFirst() for ; itr.Valid(); itr.Next() { key := itr.Key().(*Key).Slice value := itr.Value().(*Value).Slice k := makeCopy(key.Data()) v := makeCopy(value.Data()) itrResults[string(k)] = v } if len(itrResults) != len(expectedValues) { t.Fatalf("Expected [%d] results from iterator, found [%d]", len(expectedValues), len(itrResults)) } for k, v := range expectedValues { if !bytes.Equal(itrResults[k], v) { t.Fatalf("Wrong value for key [%s]. Expected [%s], found [%s]", k, itrResults[k], v) } } }

Error Message

github.com/hyperledger/fabric/core/db/rocksdb core/db/rocksdb/rocksdb_test.go:270: cannot use itr.(*DbIterator).Iterator (type *gorocksdb.Iterator) as type db.Iterator in assignment: *gorocksdb.Iterator does not implement db.Iterator (wrong type for Key method) have Key() *gorocksdb.Slice want Key() db.Keyer

最满意答案

问题不在于类型断言，你会在那里打破，因为你正在使用的实例没有实现该接口。 话虽如此，你可以通过这样做优雅地处理这个问题;

itr, ok = itr.(*DbIterator) if !ok { //try to recover }

但是，就像我说的那样当你到达那个代码时， itr的类型不是代码所期望的，所以它不会以期望的结果结束，你必须在这里做一些恢复/错误处理才能使它工作更好或弄清楚你是如何在第一时间传递错误类型的。

The problem isn't the type asserts, you're gonna break there regardless because the instance you're working with doesn't implement that interface. That being said you can handle this gracefully by doing;

itr, ok = itr.(*DbIterator) if !ok { //try to recover }

But yeah, like I said when you get to that code the type of itr is not what the code is expecting so it's not going to end with the desired result, you'll have to do some recovery/error handling here to make it work better or figure out how you're getting the wrong type passed down there in the first place.