C# Language Specification

Implicit constant expression conversions

An implicit constant expression conversion permits the following conversions:

• 
  A constant-expression (§7.19) of type int can be converted to type sbyte, byte, short, ushort, uint, or ulong, provided the value of the constant-expression is within the range of the destination type.
  
• 
  A constant-expression of type long can be converted to type ulong, provided the value of the constant-expression is not negative.
  

10. 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).

11.