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reflect: clarify behavior for unexported names #4876
Exported field names inhabit a global namespace but unexported (lower case) field names belong to the namespace of the package in which they lexically appear. The "reflect" API doesn't mention this, which can lead to surprising results when searching for a lowercase field by name. func (v Value) FieldByName(name string) Value FieldByName returns the struct field with the given name. It returns the zero Value if no field was found. It panics if v's Kind is not struct. In the example below, a struct has two fields, both called r, but belonging to different namespaces. The "reflect" algorithm, when searching for "r", finds both, and assumes there's a conflict when in reality there isn't. Without changing the existing API, that's the best we can do, but it would be useful to document this because otherwise the choice of unexported field names inside one package can have subtle effects on another package using reflection. http://play.golang.org/p/WTj5d06CQ3 (gri: I know you know all this already.)
Perhaps the most correct solution is to add another method: // Precondition: !ast.IsExported(fieldname) <=> pkgpath != "" FieldFieldByQualifiedName(pkgpath, fieldname string) which also compares the StructField.PkgPath, not just the name. The first method could be changed in one of the following ways: (a) document its tricky behaviour but remain unchanged. (b) reject lowercase field names. (b) accept lowercase field names, and in that case reflect over the callstack (!) and extract the default package name from the calling frame, and then pass that to the qualified 2-arg function.