Implicit conversions involving type parameters

The following implicit conversions exist for a given type parameter T:

· From T to its effective base class C, from T to any base class of C, and from T to any interface implemented by C. At run-time, if T is a value type, the conversion is executed as a boxing conversion. Otherwise, the conversion is executed as an implicit reference conversion or identity conversion.

· From T to an interface type I in T’s effective interface set and from T to any base interface of I. At run-time, if T is a value type, the conversion is executed as a boxing conversion. Otherwise, the conversion is executed as an implicit reference conversion or identity conversion.

· From T to a type parameter U, provided T depends on U (§10.1.5). At run-time, if U is a value type, then T and U are necessarily the same type and no conversion is performed. Otherwise, if T is a value type, the conversion is executed as a boxing conversion. Otherwise, the conversion is executed as an implicit reference conversion or identity conversion.

· From the null literal to T, provided T is known to be a reference type.

· From T to a reference type I if it has an implicit conversion to a reference type S₀ and S₀ has an identity conversion to S. At run-time the conversion is executed the same way as the conversion to S₀.

· From T to an interface type I if it has an implicit conversion to an interface or delegate type I₀ and I₀ is variance-convertible to I (§13.1.3.2). At run-time, if T is a value type, the conversion is executed as a boxing conversion. Otherwise, the conversion is executed as an implicit reference conversion or identity conversion.

If T is known to be a reference type (§10.1.5), the conversions above are all classified as implicit reference conversions (§6.1.6). If T is not known to be a reference type, the conversions above are classified as boxing conversions (§6.1.7).

User-defined implicit conversions

A user-defined implicit conversion consists of an optional standard implicit conversion, followed by execution of a user-defined implicit conversion operator, followed by another optional standard implicit conversion. The exact rules for evaluating user-defined implicit conversions are described in §6.4.4.

Anonymous function conversions and method group conversions

Anonymous functions and method groups do not have types in and of themselves, but may be implicitly converted to delegate types or expression tree types. Anonymous function conversions are described in more detail in §6.5 and method group conversions in §6.6.

Дата добавления: 2015-11-16