Hamlet

“To be, or not to be, that is the question”

Hamlet is a small .NET library that provides a simple option type, common operations for working with options (map, bind, filter...), as well as some extension methods for using Linq syntax on options.

An option type is useful to represent the presence or absence of a value. In C#, null is often used for that purpose, but it has some issues:

• it's a frequent source of bugs, because developers often forget to check for null
• null might be a valid value in some scenarios, so it doesn't really mean the same thing as an absence of value; "I have a value that is null" is not the same as "I have no value".

Most functional languages have an option type, often called Option (as in F#) or Maybe (as in Haskell). C# could also benefit from such a type, so here it is!

Usage

Creating an option

using Hamlet;

// An optional int with the value 42
Option<int> a = Option.Some(42);
// or just
Option<int> a = 42;

// An optional int with no value
Option<int> b = Option.None();
// or
var b = Option.None<int>();
// or just
Option<int> b = default;

Checking if a value is present and getting the value

Option<int> option = ...

// Explicit check
if (option.IsSome)
{
    int value = option.Value;
	...
}

// Using TryGetValue
if (option.TryGetValue(out var value))
{
    ...
}

Usage with Linq

Linq can be used to work with the value that might be contained in an option, by using projections or filters.

In the following example, result will be Some(option.Value + 1) if option has a value, and None otherwise:

using Hamlet;
using System.Linq;

Option<int> option = ...
Option<int> result =
    from value in option
    select value + 1;

In the following example, result will be Some(option.Value) if option has a value greater than 0, and None otherwise:

using Hamlet;
using System.Linq;

Option<int> option = ...
Option<int> result =
    from value in option
    where value > 0
    select value;

Values from multiple options can also be combined. In the following example, result will be Some(optA.Value + optB.Value) if both optA and optB have a value, and optB's value is greater than 0:

using Hamlet;
using System.Linq;

Option<int> optA = ...
Option<int> optB = ...
Option<int> result =
    from a in optA
    from b in optB
    where b > 0
    select a + b;

Credits

The package logo is the icon Hamlet by Priscilla Alves from the Noun Project, under license CC BY 3.0.