Method If

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.

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.