Custom operators

Operators are the ONLY place where you can define something that the code you write can NOT have variable syntax. You MUST use the syntax pre-defined for the operator you’re overriding. The table in [Operators] lists which operators can be overridden. The key here is the operator keyword. It marks what you’re declaring as an operator. List the parameter in the order they appear delimited by commas. All custom operators must be declared as members of a struct, class, interface, or enum type—even in DASIL! The sample below shows how to declare typical operators. All operators are implicitly static.

public operator - var int left, var int right
  returns int

public operator -- (\prefix\ | \postfix\) var int assign

public operator -- var ref int assign, var int delta ' This is overloaded
  returns int

public operator = var ref int assign, var int newValue ' assignment operator
  returns int

public operator = var int left , var int right ' equality
  returns boolean

Some notes:

• If the operator’s definition has a var whose type is a ref type (not just a reference), your override must have ref too. Ditto for the out operator.
• Note the unary ++ and -- will always be passed one of two special keywords that specify how the operator was called: as a prefix operator or a postfix operator.
• Most operators will return something.
• ASIL doesn’t yet define any ternary operators, but if it ever does, they will be declared as a_b where a and b are the operators. So the ?: operator from C would be written as ?_:.
• Operators can’t be generics. They can, however, be methods inside a generic type.
• If you override and, or, and not; the rest compiler will generic nor, band, xor, and xnor for you.

• As listed in the table below, some operators have two “names”. These can be override with either name.

  Name 1	Name 2
  <>	><
  >=	=>
  <=	=<

Default implementations of comparison operators

If your type implements IComparable, the compiler will generate the ==, <>, <, <=, >=, and > operators for you.