Option<T> API

Every method on Option<T>, grouped by what it does.

Option<T> holds either a value (Some<T>) or nothing (None<T>). It has no third state, and it cannot hold null.

This is the lookup. If you are learning the type rather than looking a method up, read the Option<T> guide first.

Creation

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Method	What it does
Option.Some(value)	Wraps a value. Throws on null.
Option.None<T>()	The empty case.
Option.FromNullable(value)	Some if the value is not null, None if it is.
Option.Try(factory)	Runs a factory that might throw. None if it throws or returns null.
Option.TryAsync(factory)	The same, for a factory returning a Task.

Transform

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Method	What it does
Map	Changes the value if there is one.
AndThen	Chains a step that itself returns an Option, without nesting.
Filter	Keeps the value only if it passes a predicate.
Zip	Pairs two options into one holding a tuple.
ZipWith	Pairs two options, combining them yourself.
Unzip	Splits an option holding a tuple back into two.
And	The second option, if the first was Some.
Or	The first Some of the two.
OrElse	The same, building the second only if needed.
Xor	The value only if exactly one of the two is Some.
Reduce	Merges two options of the same type.

Consume

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Member	What it does
IsSome / IsNone	The state, as a bool.
IsSomeAnd / IsNoneOr	The state combined with a predicate.
Match	Both branches, one plain value out.
Deconstruct	Lets C# pattern matching bind the value positionally.
Unwrap	The value, or an UnwrapException.
UnwrapOr	The value, or the fallback you supplied.
UnwrapOrElse	The value, or one built by a factory.
UnwrapOrDefault	The value, or default(T).
UnwrapOrNull	The value, or null. Value types only.
Expect	Like Unwrap, with your own exception message.
MapOr	Transforms the value, or returns your fallback.
MapOrElse	The same, building the fallback lazily.
MapOrDefault	The same, falling back to default(TOut).
MapOrNull	The same, falling back to null. Value types only.

Side effects

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Method	What it does
Inspect	Runs an action on the value and hands the option back unchanged.

Nesting and conversion

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Method	What it does
Flatten	Collapses an Option<Option<T>> into an Option<T>.
Transpose	Turns an Option<Result<T, E>> into a Result<Option<T>, E>.
OkOr	Converts to a Result, with an error you already have.
OkOrElse	The same, building the error only on a None.

Collections

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Method	What it does
Filter	Flips every option that fails the predicate to None.
Map	Transforms every Some in the sequence.
Flatten	Drops the Nones and keeps the values.
Collect	Some of every value, or None if any is missing.
CollectAsync	The same, over an IAsyncEnumerable.
AsEnumerable	Treats one option as a sequence of nothing or one.
FirstOrNone	The first match, or None.
FirstOr	The first match, or a fallback you supplied.
FirstOrElse	The same, building the fallback lazily.

Async

Every method above has an Async counterpart. They are extension methods on the task that wraps the option, not on the option itself — see Async.

State overloads

Most methods that take a delegate also take one that receives your data instead of capturing it. See State overloads.