Method SingleOrNone

Namespace

SodaFlow.Functional

Assembly

SodaFlow.Functional.dll

SingleOrNone<T>(IEnumerable<T>?)

Returns the only element of a sequence, if it has one.

[Pure]
public static Maybe<T> SingleOrNone<T>(this IEnumerable<T>? source)

Parameters

source IEnumerable<T>

The sequence to read. A null sequence counts as empty.

Returns

Maybe<T>

A Maybe<T> containing the single element, and one containing no value if the sequence is empty.

Type Parameters

T

The type of the values in the sequence.

Remarks

This throws where SingleOrDefault<TSource>(IEnumerable<TSource>) throws, and for the same cause: a sequence with two elements did not fail to give an answer. It contradicts the assumption that there was only one to give. A result with no value hides that. Where the caller needs more than one, and simply does not wanted, filter first, or use FirstOrNone<T>(IEnumerable<T>?). Reads at most two elements of the source.

Exceptions

InvalidOperationException

The sequence contains more than one element.

SingleOrNone<T>(IEnumerable<T>?, Func<T, bool>)

Returns the only element of a sequence which satisfies a predicate, if there is one.

[Pure]
public static Maybe<T> SingleOrNone<T>(this IEnumerable<T>? source, Func<T, bool> predicate)

Parameters

source IEnumerable<T>

The sequence to search. A null sequence counts as empty.

predicate Func<T, bool>

The condition the element must satisfy.

Returns

Maybe<T>

A Maybe<T> containing the single matching element, and one containing no value if there is none.

Type Parameters

T

The type of the values in the sequence.

Exceptions

InvalidOperationException

More than one element satisfies predicate.