Option<T>

Tango.Types.Option<T>

This type represents an optional value.

Instances of Option<T> encapsulates the value as a container and only allow access through the Match e Match2 methods.

Option values are considered in IsNone state when the encapsulated value are equals to null or equals to its default.

Properties

Constructors

Methods

Operators Overload

Usage

You can use an Option value in so many different ways.

Creating an option value

You can use the constructor to create option values in IsSome or IsNone states, according its parameter.

Constructors

Option<int> valueWithSome = new Option<int>(10); //-> IsSome
Option<int> valueWithNone = new Option<int>(0);  //-> IsNone

You can also use the static methods Some or None to define the desired state of the value. The Some method can be little tricky because it there's no guarantees that the created value will be at IsSome state, because it depends on the value passed as parameter.

Some and None methods

Option<int> valueWithSome = Option<int>.Some(10); //-> IsSome
Option<int> valueWithNone = Option<int>.Some(0);  //-> IsNone
Option<int> value2WithNone = Option<int>.None();  //-> IsNone

Finally the simplest version: implict cast. Because of this feature you don't need to worry about any kind of syntax, you just create the value as regular types.

Implicit cast

Option<int> valueWithSome = 10; //-> IsSome
Option<int> valueWithNone = 0;  //-> IsNone

Through this implicit cast you can creates new option values by using regular return commands.

See:

private Option<string> GetTextIfEven(int value)
{
  if (value % 2 == 0)
    return "Even";
  else
    return null;
}

In a more functional way:

private Option<string> GetTextIfEven(int value)
  => value % 2 == 0 ? 
      "Even" 
      : null;

Realize the fact that the method returns just a regular string or null values, without creates an Option value.

This method works fine, but is more elegant to use the None method of Option class instead of null.

private Option<string> GetTextIfEven(int value)
=> value % 2 == 0 ?
"Even"
: Option<string>.None();

Getting value from an option

To get the value encapsulated by an Option<T> method is necessary uses Match or Match2 methods. There aren't other way to get this value, so, you need to treat both cases properly.

The Match method receive two different functions as parameters, one for each case: Some and None state.

Match with named parameters

Option<int> optionalValue = 10;
int value = optionalValue.Match(
        methodWhenSome: number => number,
        methodWhenNone: () => 0);

The first method is executed when the value IsSome, because of it, this method receive an T value as parameter (int in this example).

The second method is executed when the value IsNone, because of it, there's no parameter in this method.

These two functions are just regular parameters, so, you can omit the its names.

Match

Option<int> optionalValue = 10;
int value = optionalValue.Match(
        number => number,
        () => 0);
//value = 10

Besides that, you can also apply some transformation in value before got it, like square the value:

Option<int> optionalValue = 10;
int value = optionalValue.Match(
        number => number * number,
        () => 0);
//value = 100

You can also returns any value in IsNone state, in the previous examples were used the zero value, but it isn't obrigatory.

Sometimes is necessary compare more than one Option values, this type provides the Match2 method to compare two different values instead of just one.

Match2

Option<int> optionalValue = 10;
Option<int> optionalValue2 = 15;

int value = optionalValue.Match2(
            optionalValue2,
            (number1, number2) => number1 + number2,
            () => 2);

//value = 25

In the previous sample a sum of two different Option value was made. In this particular case, both Option was in IsSome state, so the first method was executed:

(number1, number2) => number1 + number2

In this anonymous method the number1 parameter received the value from optinalValue (10) and number2 from optionalValue2(15), resulting 25.

The second method is executed when any Option value is in IsNone state.

Match2

Option<int> optionalValue = 10;
Option<int> optionalValue2 = Option<int>.None();

int value = optionalValue.Match2(
            optionalValue2,
            (number1, number2) => number1 + number2,
            () => 2);
// value = 2

There's an overload of Match and Match2 methods to receive an Action as parameter instead of a Func.

The fundamentals about Option values can be find in Fundamentals > Option Values section.