Method FallbackIfEmpty

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FallbackIfEmpty<T>(IEnumerable<T>, params T[])

Returns the elements of a sequence, but if it is empty then returns an alternate sequence from an array of values.

Declaration
public static IEnumerable<T> FallbackIfEmpty<T>(this IEnumerable<T> source, params T[] fallback)
Parameters
Type Name Description
IEnumerable<T> source

The source sequence.
T[] fallback

The array that is returned as the alternate sequence if source is empty.
Returns
Type Description
IEnumerable<T>

An IEnumerable<T> that containing fallback values if source is empty; otherwise, source.
Type Parameters
Name Description
T

The type of the elements in the sequences.
Remarks

The length of source is not evaluated until enumeration. source is enumerated; if there is at least one item, the elements of source will be streamed in a deferred manner. If there are no items in source, the items in fallback will be streamed.

Examples

The following code example demonstrates how to use FallbackIfEmpty to use a fallback sequence if the primary sequence is empty.

var flag = false;
var sequence = SuperEnumerable.Defer(
    () =>
    {
        if (flag) return Enumerable.Empty<int>();
        flag = true;
        return Enumerable.Range(1, 5);
    });

// Replace a sequence if it is empty.
var result = sequence.FallbackIfEmpty(10, 11, 12);

Console.WriteLine(
    "Non-Empty: [" +
    string.Join(", ", result) +
    "]");

Console.WriteLine(
    "Empty: [" +
    string.Join(", ", result) +
    "]");

// This code produces the following output:
// Non-Empty: [1, 2, 3, 4, 5]
// Empty: [10, 11, 12]
Exceptions
Type Condition
ArgumentNullException

source or fallback is null.
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FallbackIfEmpty<T>(IEnumerable<T>, IEnumerable<T>)

Returns the elements of a sequence, but if it is empty then returns an alternate sequence of values.

Declaration
public static IEnumerable<T> FallbackIfEmpty<T>(this IEnumerable<T> source, IEnumerable<T> fallback)
Parameters
Type Name Description
IEnumerable<T> source

The source sequence.
IEnumerable<T> fallback

The alternate sequence that is returned if source is empty.
Returns
Type Description
IEnumerable<T>

An IEnumerable<T> that containing fallback values if source is empty; otherwise, source.
Type Parameters
Name Description
T

The type of the elements in the sequences.
Remarks

The length of source is not evaluated until enumeration. source is enumerated; if there is at least one item, the elements of source will be streamed using deferred execution. If there are no items in source, then fallback will be streamed using deferred execution.

Examples

The following code example demonstrates how to use FallbackIfEmpty to use a fallback sequence if the primary sequence is empty.

var flag = false;
var sequence = SuperEnumerable.Defer(
    () =>
    {
        if (flag) return Enumerable.Empty<int>();
        flag = true;
        return Enumerable.Range(1, 5);
    });
    
// Replace a sequence if it is empty.
var result = sequence
    .FallbackIfEmpty(
        Enumerable.Range(20, 3));

Console.WriteLine(
    "Non-Empty: [" +
    string.Join(", ", result) +
    "]");

Console.WriteLine(
    "Empty: [" +
    string.Join(", ", result) +
    "]");

// This code produces the following output:
// Non-Empty: [1, 2, 3, 4, 5]
// Empty: [20, 21, 22]
Exceptions
Type Condition
ArgumentNullException

source or fallback is null.