pub trait Backend{} pub trait SupportsDefaultKeyword {} impl SupportsDefaultKeyword for Postgres {} pub struct Postgres; impl Backend for Postgres {} pub struct AstPass(::std::marker::PhantomData); pub trait QueryFragment {} #[derive(Debug, Clone, Copy)] pub struct BatchInsert<'a, T: 'a, Tab> { _marker: ::std::marker::PhantomData<(&'a T, Tab)>, } impl<'a, T:'a, Tab, DB> QueryFragment for BatchInsert<'a, T, Tab> where DB: SupportsDefaultKeyword + Backend, {}