Trait implemented to allow a type to be used as a field key.
Note: Although this is implemented for both the
Fieldtype and any type that can be borrowed as an
Fieldallows O(1) access. Indexing a field with a string results in an iterative search that performs string comparisons. Thus, if possible, once the key for a field is known, it should be used whenever possible.
Attempts to convert
&self into a
Field with the specified
metadata defines this field, then the field is returned. Otherwise,