github.com/imdariO/mergo (go): Package mergo merges same-type structs and maps by setting default values in zero-value fields.  Mergo won't merge unexported (private) fields but will do recursively any exported one. It also won't merge structs inside maps (because they are not addressable using Go reflection).  From my own work-in-progress project:
Keywords: go|golang|hacktoberfest|mapping|merge|structures