Datasheet

ManualsBrandsWiley ManualsSoftware978-0-470-52801-3

Type Inference

C# 3.0 provides some of this, via the automatic property declaration — it assumes the task of creat-

ing a ﬁ eld and the get/set logic to return and assign to that ﬁ eld, respectively, but unfortunately,

C# 3.0 will choke on the

var declaration as a method parameter or as a ﬁ eld. And 3.0 allows only

inference for local variable declarations — any attempt to use these things as ﬁ elds in an object will

require the explicit declaration and, potentially, all the disconcerting angle brackets.

Additionally, looking at the previous example, some of C#’s syntactic legacy begins to look awk-

ward — speciﬁ cally, the use of the

var as a type preﬁ x is somewhat redundant if the compiler is

going to infer the type directly, so why continue to use it?

// This is not legal C# 3.0

class Person

{

public Person(firstName, lastName, age)

{

FirstName = firstName;

LastName = lastName;

Age = age;

}

public FirstName { get; set; }

public LastName { get; set; }

public Age { get; set; }

public FullName {

get { return FirstName + “ “ + LastName; }

}

Despite the compiler’s best efforts, though, it may be necessary to provide the type as a way of

avoiding ambiguity, such as when the compiler cannot infer the type or ﬁ nds any number of poten-

tial inferences.

FirstName and LastName can be assumed to be strings, since the FullName property

adds them together against a

constant string, something (presumably) only strings can do. Age,

however, is an ambiguity: It could be just about any object type in the system, because it is never

used in a context that enables the compiler to infer its numerical status. As a result, the compiler

needs a small bit of help to get everything right.

If the type declaration preﬁ x syntax has been thrown away, though, then something else will have to

take its place, such as an optional type declaration sufﬁ x syntax: