Method TrySingle

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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.
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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.
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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.