英文:
Assigning to copy of a map seems to be modifying the original
问题
我有一个变量decodedToken（类型为struct），我通过类型断言访问它的一个名为"Claims"的值：
claims := decodedToken.Claims.(jwt.MapClaims)
然后，我循环遍历claims（类型为map[string]interface{}），并直接修改它的值：
for key := range claims {
claims[key] = "modified" + key
}
因此，我期望原始的decodedToken变量不会改变，因为我只是对claims变量进行了操作。然而，decodedToken也被修改成了我修改后的值。
我的问题是为什么会这样，以及如何保持decodedToken不变？
英文:
I have a variable decodedToken (type: struct), and I access one of its values called "Claims" through a type assertion:
claims := decodedToken.Claims.(jwt.MapClaims)
I then loop through the claims (type: map[string]interface{}), and modify its values in place:
for key := range claims {
claims[key] = "modified"+key
}
Hence, I expect that the original decodedToken variable would be unchanged, since I have just performed an operation on the claims variable. However, decodedToken is also changed to my modified value.
My question is why is this so, and how do I leave the decodedToken untouched?
答案1
得分: 1
由于claims是一个引用类型，类似于map或slice。
解决方案是对任何引用数据进行深拷贝。不幸的是，Go语言没有一种通用的方式来深拷贝任何map。所以你需要自己实现。
或者更实际的做法是创建一个新的对象（变量）来存储修改后的decodedToken。
另外，在同一语句中迭代一个map并修改其值是不好的做法。
英文:
Since claims is a reference type, like a map or slice.
The solution is make a deep copy of any referenced data. Unfortunately there are no universal way to make a deep copy of any map in Go. So you should make your own.
Or more practical way to do your job is making a new object(variable) to contain the modified decodedToken.
Also, it's not good to iterated a map and modify its value in a same statement.
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