英文:
Thrift go support of map with struct value as key
问题
我使用Thrift 0.9.1进行了Golang生成的实验，例如：
Thrift定义如下：
struct AppIdLeveledHashKeyTimeKeyHour {
1: required i32 appId
2: required LeveledHashKey leveledHashKey
3: required TimeKeyHour timeKeyHour
}
typedef map<AppIdLeveledHashKeyTimeKeyHour, ...sth else...> EventSliceShardIdValue
在生成的代码中，EventSliceShardIdValue会变成：
type EventSliceShardIdValue map[*AppIdLeveledHashKeyTimeKeyHour]EventSliceAppIdLeveledHashKeyTimeKeyHourValue
你可以看到，关键部分是一个指针，表示内存地址。在Golang中，大多数情况下，将指针作为map的键（而不是值或对象的哈希值）是没有意义的。要将一些字段的组合作为map的键，定义应该使用值类型，如：
map[AppIdLeveledHashKeyTimeKeyHour]EventSliceAppIdLeveledHashKeyTimeKeyHourValue
这是Thrift的Golang支持的问题（或者我误用了某些东西）吗？有没有解决这个问题的方法？
英文:
I experimented golang generation with Thrift 0.9.1, for example,
thrift definition,
struct AppIdLeveledHashKeyTimeKeyHour {
1: required i32 appId
2: required LeveledHashKey leveledHashKey
3: required TimeKeyHour timeKeyHour
}
typedef map<AppIdLeveledHashKeyTimeKeyHour, ...sth else...> EventSliceShardIdValue
in the generated code, EventSliceShardIdValue would be,
type EventSliceShardIdValue map[*AppIdLeveledHashKeyTimeKeyHour]EventSliceAppIdLeveledHashKeyTimeKeyHourValue
you can find the key part is a pointer which represents memory address. In golang a pointer as map key (instead of a value, or hash of the obj) is useless in most cases. To use a combination of some fields as map key, the definition should use a value type like
map[AppIdLeveledHashKeyTimeKeyHour]EventSliceAppIdLeveledHashKeyTimeKeyHourValue
Is it a problem of Thrift's go support (or I misused sth)? Any workaround to solve this problem in thrift?
答案1
得分: 0
结构体（不包含指针）只能在某些有限的情况下用作映射键（根据http://golang.org/ref/spec#Comparison_operators，它们必须是可比较的）；可能AppIdLeveledHashKeyTimeKeyHour不符合这个定义，所以实际上无法在不使用指针作为键的情况下构建映射。
英文:
Structs (without pointers) can only be used as map keys under certain limited circumstances (they must be comparable per http://golang.org/ref/spec#Comparison_operators); it's possible that AppIdLeveledHashKeyTimeKeyHour doesn't fit this definition, so it's not actually possible to build a map without using a pointer for the key.
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