CONVERSIONS AND PROMOTIONS

Casting Conversion

5.5

5.4   String Conversion

String conversion applies only to the operands of the binary

+

 operator when one

of the arguments is a

String

. In this single special case, the other argument to the

+

 is converted to a

String

, and a new

String

 which is the concatenation of the

two strings is the result of the

+

. String conversion is specified in detail within the

description of the string concatenation

+

 operator ( 15.17.1).

5.5   Casting Conversion

Sing away sorrow, cast away care.

 Miguel de Cervantes (1547 1616),

Don Quixote

 (Lockhart s translation), Chapter viii

Casting conversion

 is applied to the operand of a cast operator ( 15.15): the type

of the operand expression must be converted to the type explicitly named by the

cast operator. Casting contexts allow the use of an identity conversion ( 5.1.1), a

widening primitive conversion ( 5.1.2), a narrowing primitive conversion

( 5.1.3), a widening reference conversion ( 5.1.4), or a narrowing reference con 

version ( 5.1.5). Thus casting conversions are more inclusive than assignment or

method invocation conversions: a cast can do any permitted conversion other than

a string conversion.

Some casts can be proven incorrect at compile time; such casts result in a

compile time error.

A value of a primitive type can be cast to another primitive type by identity

conversion, if the types are the same, or by a widening primitive conversion or a

narrowing primitive conversion.

A value of a primitive type cannot be cast to a reference type by casting con 

version, nor can a value of a reference type be cast to a primitive type.

The remaining cases involve conversion between reference types. The

detailed rules for compile time correctness checking of a casting conversion of a

value of compile time reference type

S

 (source) to a compile time reference type

T

 (target) are as follows:

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