Method TrySingle

TrySingle<T, TCardinality>(IEnumerable<T>, TCardinality, TCardinality, TCardinality)

Returns a tuple with the cardinality of the sequence and the single element in the sequence if it contains exactly one element. similar to Single<TSource>(IEnumerable<TSource>).

Declaration

public static (TCardinality Cardinality, T? Value) TrySingle<T, TCardinality>(this IEnumerable<T> source, TCardinality zero, TCardinality one, TCardinality many)

Parameters

Type	Name	Description
IEnumerable<T>	source	The source sequence.
TCardinality	zero	The value that is returned in the tuple if the sequence has zero elements.
TCardinality	one	The value that is returned in the tuple if the sequence has a single element only.
TCardinality	many	The value that is returned in the tuple if the sequence has two or more elements.

Returns

Type	Description
(TCardinality Cardinality, T Value)	A tuple containing the identified TCardinality and either the single value of T in the sequence or its default value.

Type Parameters

Name	Description
T	The type of the elements of source.
TCardinality	The type that expresses cardinality.

Remarks

This operator uses immediate execution, but never consumes more than two elements from the sequence.

Examples

The following code example demonstrates how to evaluate the cardinality of a sequence using TrySingle.

// Determine cardinality of sequence
var result = Enumerable.Range(1, 0).TrySingle("none", "one", "many");
Console.WriteLine(result.ToString());

result = Enumerable.Range(1, 1).TrySingle("none", "one", "many");
Console.WriteLine(result.ToString());

result = Enumerable.Range(1, 10).TrySingle("none", "one", "many");
Console.WriteLine(result.ToString());

// This code produces the following output:
// (none, 0)
// (one, 1)
// (many, 0)

Exceptions

Type	Condition
ArgumentNullException	source is null.

TrySingle<T, TCardinality, TResult>(IEnumerable<T>, TCardinality, TCardinality, TCardinality, Func<TCardinality, T?, TResult>)

Returns a result projected from the the cardinality of the sequence and the single element in the sequence if it contains exactly one element.

Declaration

public static TResult TrySingle<T, TCardinality, TResult>(this IEnumerable<T> source, TCardinality zero, TCardinality one, TCardinality many, Func<TCardinality, T?, TResult> resultSelector)

Parameters

Type	Name	Description
IEnumerable<T>	source	The source sequence.
TCardinality	zero	The value that is passed as the first argument to resultSelector if the sequence has zero elements.
TCardinality	one	The value that is passed as the first argument to resultSelector if the sequence has a single element only.
TCardinality	many	The value that is passed as the first argument to resultSelector if the sequence has two or more elements.
Func<TCardinality, T, TResult>	resultSelector	A function that receives the cardinality and, if the sequence has just one element, the value of that element as argument and projects a resulting value of type TResult.

Returns

Type	Description
TResult	The value returned by resultSelector.

Type Parameters

Name	Description
T	The type of the elements of source.
TCardinality	The type that expresses cardinality.
TResult	The type of the result value returned by the resultSelector function.

Remarks

This operator uses immediate execution, but never consumes more than two elements from the sequence.

Examples

The following code example demonstrates how to evaluate the cardinality of a sequence using TrySingle.

// Determine cardinality of sequence
var result = Enumerable.Range(10, 0).TrySingle(0, 1, 2, (count, one) => count switch { 0 => "no elements", 1 => $"single({one})", 2 => "many elements" });
Console.WriteLine(result);

result = Enumerable.Range(10, 1).TrySingle(0, 1, 2, (count, one) => count switch { 0 => "no elements", 1 => $"single({one})", 2 => "many elements" });
Console.WriteLine(result);

result = Enumerable.Range(10, 10).TrySingle(0, 1, 2, (count, one) => count switch { 0 => "no elements", 1 => $"single({one})", 2 => "many elements" });
Console.WriteLine(result);

// This code produces the following output:
// no elements
// single(10)
// many elements

Exceptions

Type	Condition
ArgumentNullException	source or resultSelector is null.

TrySingle<TSource>(IEnumerable<TSource>)

Returns the single element in the sequence if it contains exactly one element. Similar to SingleOrDefault<TSource>(IEnumerable<TSource>).

Declaration

public static TSource? TrySingle<TSource>(this IEnumerable<TSource> source)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.

Returns

Type	Description
TSource	The single element or the default value of TSource.

Type Parameters

Name	Description
TSource	The type of the elements of source.