Discriminated unions provide support for values that can be one of several named cases, possibly each with different values and types. Discriminated unions are useful for heterogeneous data;
Discriminated unions allow you to build up complex data structures representing a well-defined set of choices. For example, you need to build an implementation of a choice variable, which has two values yes and no. Using the Union's tool, you can design this.
[ attributes ]
type [accessibility-modifier] type-name =
| case-identifier1 [of [ fieldname1 : ] type1 [ * [ fieldname2 : ] type2 ...]
| case-identifier2 [of [fieldname3 : ]type3 [ * [ fieldname4 : ]type4 ...]
[ member-list ]
The following example declares a Shape type.
type Shape =
| Rectangle of width : float * length : float
| Circle of radius : float
| Prism of width : float * float * height : float
The above code declares a discriminated union Shape, which can have values of three cases: Rectangle, Circle, and Prism. Each case has a different set of fields.
You construct objects by providing values for the named and anonymous fields, as shown below.
let rect = Rectangle( width = 6.0, length = 10.0)
let circ = Circle (2.5)
let prism = Prism(3.75, 4.0, height = 5.0)
Circle case code.Now let's see how to call and set values for these cases.
type Shape =
| Rectangle of width : float * length : float
| Circle of radius : float
| Prism of width : float * float * height : float
let compute vall =
match vall with
| Rectangle (val1, val2) -> val1*val2
| Circle (val1)->val1*val1*3.1415
| Prism (val1, val2, val3)->val1*val2*val3
let rect = compute (Rectangle( width = 6.0, length = 10.0))
let circ = compute (Circle (2.5))
let prism = compute (Prism(3.75, 4.0, height = 5.0))
Console.WriteLine(rect)
Console.WriteLine(circ)
Console.WriteLine(prism)