support default impl for specialization (original) (raw)

rust-lang/rfcs#1210 included support for default impl, which declared a set of defaults that other impls can inherit (if they correspond to a subset of the default impl's types). This was intended as a replacement/improvement of the existing default methods that appear in trait bodies (it was also originally called partial impl). Unfortunately, this feature is not yet implemented!

Some things to be sure of:

• a default impl need not include all items from the trait
• a default impl alone does not mean that a type implements the trait
• all items in a default impl are (implicitly) default and hence specializable

cc #31844