Why Can\'t I Directly Modify Struct Fields in Go Maps?

Can't Modify Map Values: Understanding Addressability

When dealing with maps in Go, you may encounter an error stating "can not assign to it." This occurs when you attempt to modify a struct field within a map value directly.

Understanding Addressability

In Go, addressability refers to the ability to obtain the memory address of a variable. Addressable variables allow for value changes through pointer manipulation. However, map values are not addressable. This allows map implementations to move values around memory as needed, optimizing performance.

Reason for Error

When you try to assign a value to a struct field using the selector (.) operator, the struct must be addressable. Since map values are not addressable, this operation is prohibited.

Solutions

There are two solutions to this issue:

• Use a Pointer as Map Value: Store a pointer to the struct instead of the struct itself in the map. By using a pointer, the addressability requirement is met, and you can modify the struct fields.
• Copy or Replace Map Value: Create a copy of the existing struct value, modify it, and assign it back to the map. Alternatively, you can replace the map value with an entirely new struct.

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