[−][src]Trait pergola::DefTraits
DefTraits is used to constrain LatticeDefs and also type parameters
of structs that implement LatticeDef. This requires some explaining.
A LatticeDef is typically just a unit-struct with no content aside from
PhantomData -- it's essentially a module to be used as a parameter to a
LatticeElt -- so it doesn't obviously make sense to constrain them at all.
But: since LatticeDefs wind up as type parameters for a variety of
structs in client libraries (that themselves contain LatticeElts that
use those LatticeDefs), any attempt to derive standard traits on such
structs will bump into a bug in
derive which prevents
derived impls from working right if a struct's type parameters don't
themselves implement the derived traits.
So to keep derive working downstream, we insist all LatticeDefs provide
most standard derivable traits. Impls for them can be derived on the
LatticeDefs trivially anyways, so this isn't much of a burden.