Concepts of Programming Languages

9.9 Generic Subprograms 427

9.9.3 Generic Methods in C# 2005

The generic methods of C# 2005 are similar in capability to those of Java 5.0,

except there is no support for wildcard types. One unique feature of C# 2005

generic methods is that the actual type parameters in a call can be omitted if the

compiler can infer the unspecified type. For example, consider the following

skeletal class definition:

class MyClass {

public static T DoIt<T>(T p1) {

...
}
}

The method DoIt can be called without specifying the generic parameter if

the compiler can infer the generic type from the actual parameter in the call.

For example, both of the following calls are legal:

int myInt = MyClass.DoIt(17); // Calls DoIt<int>

string myStr = MyClass.DoIt('apples');

// Calls DoIt<string>

9.9.4 Generic Functions in F#

The type inferencing system of F# is not always able to determine the type of

parameters or the return type of a function. When this is the case, for some

functions, F# infers a generic type for the parameters and the return value.

This is called automatic generalization. For example, consider the following

function definition:

let getLast (a, b, c) = c;;

Because no type information was included, the types of the parameters and

the return value are all inferred to be generic. Because this function does not

include any computations, this is a simple generic function.

Functions can be defined to have generic parameters, as in the following

example:

let printPair (x: 'a) (y: 'a) =

printfn "%A %A" x y;;

The %A format specification is for any type. The apostrophe in front of the type

named a specifies it to be a generic type.^9 This function definition works (with

generic parameters) because no type-constrained operation is included.

9. There is nothing special about a—it could be any legal identifier. By convention, lowercase
   letters at the beginning of the alphabet are used.