How to Modify Struct Fields within Map Values in Go?

Assigning to Struct Fields in Map Values

When dealing with maps in Go, one may encounter issues with assigning to struct fields within map values. This occurs when one tries to directly modify a map value's struct field, resulting in the error: "cannot assign to struct field in a map."

To resolve this issue and successfully modify struct fields in map values, an important principle to understand is value assignment semantics in Go. When a map key is accessed, its associated value is a copy of the original value. As such, direct modifications to this copy will not be reflected in the original value in the map.

To modify struct fields in map values effectively, the following workaround can be employed:

1. Obtain a temporary copy of the map value's struct. For instance:

   tmp := snapshots["test"].Users

2. Make the modifications to this temporary copy.

   tmp = append(tmp, user)

3. Reassign the temporary copy to the map value's struct.

   snapshots["test"].Users = tmp

Furthermore, it's worth noting that declaring the map with a pointer type (e.g., snapshots := make(map[string]*Snapshot, 1)) does not alleviate this issue.

The above is the detailed content of How to Modify Struct Fields within Map Values in Go?. For more information, please follow other related articles on the PHP Chinese website!