Generics
Features of the routine type can be generic. That means they can be defined with type parameters that need to be replaced by actual types when the feature is called.
Generic List Example
Here is the list example from section References
extended with
generic type parameters. These type parameters are then used to create a list
of i32 elements and a list of String elements.
Compatibility of Generic Types
Two types that differ only in the actual generic parameters are incompatible
in Fuzion. This means, e.g., that a value of
type array String cannot be assigned to a field of
type array Any. This avoids run-time errors such as the
infamous ArrayStoreException found in Java.
Constrained Generic Types
Generic types can be constrained as shown in this example:
It is possible to call any feature of the constraint:
Free Types
The kind of type parameters seen above, where the type parameter
is explicitly declared as a parameter of a feature is called a
Open Generic Types
Fuzion allows the definition of open generic types, i.e., generic types that can be replaced by an arbitrary number of actual generic types. Open Generic types are seldom useful in application code, but they provide a powerful mechanism to define Choice Types , Functions and Tuples using generic Fuzion features.
As an example from the standard library, this is the code for a Function:
Function(R type, A type...) ref is call(a A) R => abstract
Function declares an abstract feature call that
returns a result of type R specified as a generic argument and that
receives zero or more arguments defined by the open generic
argument A....
Fields of an open generic type can be accessed for instances with actual
generic parameters that are not open. Since there might be an arbitrary number
of actual generic types, there might be an arbitrary number of such
fields. Field accesses therefore require
discriminators .0, .1, etc. to select the field
corresponding to the first, second, etc. actual generic argument See
Tuples
for an example of how this is done.