opt

A C# library that mimics F#'s optionals. Since the functionality and in most cases even the method names are directly taken from F#, go check out the documentation there for details.

Changelog

Features

Methods for creating optionals are located on the Opt class. Methods like Map or Bind are available as extension methods on IOpt instances for easy chaining.

IOpt are immutable reference-types. Comparing them with Equals will be true if the both contain a value and those values are equal. Comparing IOpt with == will compare them using reference equality.

IOpt implements IEnumerable and supports Linq extensions such as Contains, Count, Any and ToArray as well as use in foreach statements.

Optional instantiation

• Some Creates a present optional
• None Creates a missing optional
• FromNullable Creates an optional from a nullable, which will be missing if the given value is null
• FromOp Creates an optional from an operation that might fail (throw an exception)

Optional extension methods

• IsSome Checks if the optional is present
• IsNone Checks if the optional is missing
• Get Attempts to get the value from the optional and throws an exception if the value is missing
• DefaultValue Gets the value from this optional or a replacement if it is missing
• Map Maps an optional from one type to another using a mapping-function
• Bind Maps an optional from one type to another using a mapping-function which itself produces an optional
• Match Executes either a onSome or onNone action depending on if the optional is present
• Iter Executes the given action if the optional is present, passing in the contained value
• DefaultWith Gets the value or the result of the replacement-function if it is missing
• Filter Filters the optional with a predicate
• Flatten Collapses a nested optional into a flat one
• Fold/FoldBack Executes a folder-function with the value if present
• ForAll Checks if the value in the optional satisfies a predicate. Returns true if the optional is missing

Pattern matching

You can use C# pattern-matching on IOpt instances to check if they have a value or not.

For example:

switch (x) // Where x is an IOpt<int> { case ISome<int> { Value: var value}: // value is an int break; case INone<int> : break; }

Utility extensions

Opt also includes some utility extensions for existing types

IDictionary

• TryGet Attempts to get a value from the dictionary

IEnumerable

• TryFirst Attempts to get the first element from the sequence
• TryLast Attempts to get the last element from the sequence
• TryElementAt Attempts to get an element from the sequence by its index
• Choose Selects and maps all items in the sequence where the given choose function returned some
• TryFind Attempts to get the first item in the sequence for which the given predicate holds
• TryFindBack Attempts to get the last item in the sequence for which the given predicate holds
• Collect Collects a sequence of optionals
• TrySingle Attempts to get the only item in this collection
• FilterSome Filters out any missing values and returns only the present ones
• TryMax Attempts to get the maximum element from the collection
• TryMin Attempts to get the minimum element from the collection
• TryMaxBy Attempts to get the maximum element from the collection according to a selector function
• TryMinBy Attempts to get the minimum element from the collection according to a selector function