The Fortress Language Specification - CiteSeerX

the dynamic type of the value the expression evaluates to (unlike a type ascription described in Section 13.30). It is
usually for accessing methods provided by supertraits. When multiple supertraits provide different methods with the
same name, a subtrait may access a particular method from one of the supertraits using a type assumption. The static
type of the supertrait indicates whether a definition of the method is provided by the supertrait. If the concrete method
is not provided exist, it is a static error. The keyword super in the Java Programming Language is an example of a
type assumption.
13.32 Expression-like Functions
For convenience, the Fortress standard libraries provide functions such as cast and instanceOf that are often provided
by other programming languages.
13.32.1 Casting
Although there is no “casting” operator (equivalent to casts in the Java Programming Language) built into Fortress,
the effect of a cast can be provided by the following function:
castT(x) :T =
typecase x in
T ⇒ x
else ⇒throw CastException
end
The function converts the type of its argument to a given type. If the static type of the argument is not a subtype of
the given type, a CastException is thrown. For convenience, the function cast is included in the Fortress standard
libraries.
13.32.2 Instanceof Testing
Although there is no “instanceof” operator (equivalent to instanceof testing in the Java Programming Language) built
into Fortress, the effect of an instanceof testing can be provided by the following function:
instanceOf T(x) :Boolean =
typecase x in
T ⇒ true
else ⇒ false
end
The function tests whether its argument has a given type and returns a boolean value. For convenience, the function
instanceOf is included in the Fortress standard libraries.
13.32.3 Ignoring Values
For convenience, the function ignore (equivalent to the ignore function in the Objective Caml programming language)
is included in the Fortress standard libraries:
ignore(x) = ()
The function discards the value of its argument and returns () . For example, the following:
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