Why Doesn't Direct Method Invocation Work on Map Elements in Go, and How Can I Fix It?

Pointer Method Invocation on Map Elements

In Go, maps are powerful data structures used to store key-value pairs. However, accessing method pointers of map values can sometimes encounter errors.

Consider the following code:

<br>x:= odsMap[segRef]<br>x.GetValue("@OriginDestinationKey")<br>

This code successfully accesses the method GetValue of the value associated with the key segRef in the map odsMap. However, the following code fails:

<br>odsMap[segRef].GetValue("@OriginDestinationKey")<br>

The error messages indicate an inability to take the address of odsMap[segRef]. This occurs because map index expressions are not addressable. As maps can dynamically change during insertion, the internals may be rearranged, making address pointers unreliable.

To overcome this issue, consider the following options:

Storing Pointer Values in the Map:

Store pointers to values in the map instead of non-pointers. This eliminates the need to take the address when invoking method pointers, as pointers are already addressable.

Using Intermediate Variables:

Assign map values to intermediate variables and call method pointers on those variables. Be cautious of potential modifications to struct fields or pointed objects, as these changes may not be reflected in the map value.

Conclusion:

When dealing with maps containing values with pointer methods, it's generally advisable to use pointer values within the map. This avoids the addressability issue and ensures that pointer methods can be invoked without errors.

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