Why Can't I Take the Address of a Go Map Element?

Understanding the "Cannot Take Address of Map Element" Error

In Go, accessing the value of a map element using the expression odsMap[segRef].GetValue can lead to errors, such as "cannot call pointer method on odsMap[segRef]" and "cannot take the address of odsMap[segRef]". This occurs during compilation time when the map's internal structure is potentially modified upon adding new entries.

Explanation

Map index expressions, such as odsMap[segRef], return a non-pointer type. When attempting to call a method that requires a pointer receiver on a non-pointer value, Go's仕様禁止获取该非指针值的地址，导致编译时错误。

Workarounds

To resolve this issue, consider the following workarounds:

• Store Pointer Values in Map: Instead of storing non-pointer values in the map, store pointer values. This eliminates the need to take the address of index expressions because pointers are already pointers.
• Use a Local Variable: Assign the value of the map index expression to a local variable, and then take the address of that variable to call the pointer method. However, be mindful of potential modifications to the pointed object that may not be reflected in the map's stored value if the method has a pointer receiver.

Best Practice

If a value has methods with a pointer receiver, it is generally more efficient to use it as a pointer value rather than a non-pointer value. This simplifies addressing and method invocation while avoiding potential issues with non-pointer values.

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