Lower-bound inferences

A lower-bound inference from a type U to a type V is made as follows:

· If V is one of the unfixed X_i then U is added to the set of lower bounds for X_i.

· Otherwise, sets U₁…U_k and V₁…V_k are determined by checking if any of the following cases apply:

· V is an array type V₁[…]and U is an array type U₁[…] (or a type parameter whose effective base type is U₁[…]) of the same rank

· V is one of IEnumerable<V₁>, ICollection<V₁> or IList<V₁> and U is a one-dimensional array type U₁[](or a type parameter whose effective base type is U₁[])

· V is the type V₁? and U is the type U₁?

· V is a constructed class, struct, interface or delegate type C<V₁…V_k> and there is a unique type C<U₁…U_k> such that U (or, if U is a type parameter, its effective base class or any member of its effective interface set) is identical to, inherits from (directly or indirectly), or implements (directly or indirectly) C<U₁…U_k>.

(The “uniqueness” restriction means that in the case interface C<T>{} class U: C<X>, C<Y>{}, then no inference is made when inferring from U to C<T> because U₁ could be X or Y.)

If any of these cases apply then an inference is made from each U_i to the corresponding V_i as follows:

· If U_i is not known to be a reference type then an exact inference is made

· Otherwise, if U is an array type then a lower-bound inference is made

· Otherwise, if V is C<V₁…V_k> then inference depends on the i-th type parameter of C:

· If it is covariant then a lower-bound inference is made.

· If it is contravariant then an upper-bound inference is made.

· If it is invariant then an exact inference is made.

· Otherwise, no inferences are made.