Method If

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If<TResult>(Func<bool>, IEnumerable<TResult>)

Returns an enumerable sequence if the evaluation result of the given condition is true, otherwise returns an empty sequence.

Declaration
public static IEnumerable<TResult> If<TResult>(Func<bool> condition, IEnumerable<TResult> thenSource)
Parameters
Type Name Description
Func<bool> condition

Condition to evaluate.
IEnumerable<TResult> thenSource

Sequence to return in case the condition evaluates true.
Returns
Type Description
IEnumerable<TResult>

The given input sequence if the condition evaluates true; otherwise, an empty sequence.
Type Parameters
Name Description
TResult

Result sequence element type.
Remarks

condition is not evaluated until enumeration. If the value is true, then thenSource is enumerated. Otherwise, the sequence will be empty.

Examples

The following code example demonstrates how to selectively enumerate a sequence using If.

var sequence = Enumerable.Range(1, 5);

// Use a function to select which sequence to return values from.
var selector = true;
var result = SuperEnumerable
    .If(
        () => selector,
        sequence);

Console.WriteLine($"Selector: {selector}; result.Count(): {result.Count()}.");
selector = false;
Console.WriteLine($"Selector: {selector}; result.Count(): {result.Count()}.");
selector = true;
Console.WriteLine($"Selector: {selector}; result.Count(): {result.Count()}.");

// This code produces the following output:
// Selector: True; result.Count(): 5.
// Selector: False; result.Count(): 0.
// Selector: True; result.Count(): 5.
Exceptions
Type Condition
ArgumentNullException

condition or thenSource is null.
| Edit this page

If<TResult>(Func<bool>, IEnumerable<TResult>, IEnumerable<TResult>)

Returns an enumerable sequence based on the evaluation result of the given condition.

Declaration
public static IEnumerable<TResult> If<TResult>(Func<bool> condition, IEnumerable<TResult> thenSource, IEnumerable<TResult> elseSource)
Parameters
Type Name Description
Func<bool> condition

Condition to evaluate.
IEnumerable<TResult> thenSource

Sequence to return in case the condition evaluates true.
IEnumerable<TResult> elseSource

Sequence to return in case the condition evaluates false.
Returns
Type Description
IEnumerable<TResult>

If the condition evaluates true, then the sequence represented by thenSource; otherwise the sequence represented by elseSource.
Type Parameters
Name Description
TResult

Result sequence element type.
Remarks

condition is not evaluated until enumeration. If the value is true, then thenSource is enumerated. Otherwise, elseSource will be enumerated.

Examples

The following code example demonstrates how to selectively enumerate a sequence using If.

var sequence1 = Enumerable.Range(1, 5);
var sequence2 = Enumerable.Range(1, 10);

// Use a function to select which sequence to return values from.
var selector = true;
var result = SuperEnumerable
    .If(
        () => selector,
        sequence1,
        sequence2);

Console.WriteLine($"Selector: {selector}; result.Count(): {result.Count()}.");
selector = false;
Console.WriteLine($"Selector: {selector}; result.Count(): {result.Count()}.");
selector = true;
Console.WriteLine($"Selector: {selector}; result.Count(): {result.Count()}.");

// This code produces the following output:
// Selector: True; result.Count(): 5.
// Selector: False; result.Count(): 10.
// Selector: True; result.Count(): 5.
Exceptions
Type Condition
ArgumentNullException

condition, thenSource, or elseSource is null.