Method Do

Do<TSource>(IEnumerable<TSource>, Action<TSource>)

Lazily invokes an action for each value in the sequence.

Declaration

public static IEnumerable<TSource> Do<TSource>(this IEnumerable<TSource> source, Action<TSource> onNext)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	Source sequence.
Action<TSource>	onNext	Action to invoke for each element.

Returns

Type	Description
IEnumerable<TSource>	Sequence exhibiting the specified side-effects upon enumeration.

Type Parameters

Name	Description
TSource	Source sequence element type.

Remarks

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to lazily invoke actions for each element using Do.

var sequence = Enumerable.Range(1, 5);
            
// Execute an action for each element
var result = sequence
    .Do(i => Console.Write($"{i}, "));
    
Console.WriteLine("Before");
result.Consume();
Console.WriteLine("After");

// This code produces the following output:
// Before
// 1, 2, 3, 4, 5, After

Exceptions

Type	Condition
ArgumentNullException	source or onNext is null.

Do<TSource>(IEnumerable<TSource>, Action<TSource>, Action)

Lazily invokes an action for each value in the sequence, and executes an action for successful termination.

Declaration

public static IEnumerable<TSource> Do<TSource>(this IEnumerable<TSource> source, Action<TSource> onNext, Action onCompleted)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	Source sequence.
Action<TSource>	onNext	Action to invoke for each element.
Action	onCompleted	Action to invoke on successful termination of the sequence.

Returns

Type	Description
IEnumerable<TSource>	Sequence exhibiting the specified side-effects upon enumeration.

Type Parameters

Name	Description
TSource	Source sequence element type.

Remarks

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to lazily invoke actions for each element using Do.

var sequence = Enumerable.Range(1, 5);
            
// Execute an action for each element, and on completion
var result = sequence
    .Do(
        i => Console.Write($"{i}, "),
        () => Console.WriteLine("Completed"));
    
Console.WriteLine("Before");
result.Consume();
Console.WriteLine("After");

// This code produces the following output:
// Before
// 1, 2, 3, 4, 5, Completed
// After

Exceptions

Type	Condition
ArgumentNullException	source, onNext, or onCompleted is null.

Do<TSource>(IEnumerable<TSource>, Action<TSource>, Action<Exception>)

Lazily invokes an action for each value in the sequence, and executes an action upon exceptional termination.

Declaration

public static IEnumerable<TSource> Do<TSource>(this IEnumerable<TSource> source, Action<TSource> onNext, Action<Exception> onError)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	Source sequence.
Action<TSource>	onNext	Action to invoke for each element.
Action<Exception>	onError	Action to invoke on exceptional termination of the sequence.

Returns

Type	Description
IEnumerable<TSource>	Sequence exhibiting the specified side-effects upon enumeration.

Type Parameters

Name	Description
TSource	Source sequence element type.

Remarks

The exception is caught and passed to onNext, and then it is re-thrown. Appropriate error-handling is still required in order to safely consume the sequence.

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to lazily invoke actions for each element using Do.

var sequence = Enumerable.Range(1, 4).Concat(SuperEnumerable.Throw<int>(new InvalidOperationException()));
            
// Execute an action for each element, on error, and on completion
var result = sequence
    .Do(
        i => Console.Write($"{i}, "),
        ex => Console.WriteLine("Failed: " + ex.Message));
    
Console.WriteLine("Before");
try
{
    result.Consume();
}
catch (InvalidOperationException) {}
Console.WriteLine("After");

// This code produces the following output:
// Before
// 1, 2, 3, 4, Failed: Operation is not valid due to the current state of the object.
// After

Exceptions

Type	Condition
ArgumentNullException	source, onNext, or onError is null.

Do<TSource>(IEnumerable<TSource>, Action<TSource>, Action<Exception>, Action)

Lazily invokes an action for each value in the sequence, and executes an action upon successful or exceptional termination.

Declaration

public static IEnumerable<TSource> Do<TSource>(this IEnumerable<TSource> source, Action<TSource> onNext, Action<Exception> onError, Action onCompleted)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	Source sequence.
Action<TSource>	onNext	Action to invoke for each element.
Action<Exception>	onError	Action to invoke on exceptional termination of the sequence.
Action	onCompleted	Action to invoke on successful termination of the sequence.

Returns

Type	Description
IEnumerable<TSource>	Sequence exhibiting the specified side-effects upon enumeration.

Type Parameters

Name	Description
TSource	Source sequence element type.

Remarks

The exception is caught and passed to onNext, and then it is re-thrown. Appropriate error-handling is still required in order to safely consume the sequence.

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to lazily invoke actions for each element using Do.

var flag = false;
var sequence = SuperEnumerable.If(
    () => flag,
    Enumerable.Range(1, 5),
    Enumerable.Range(1, 4).Concat(SuperEnumerable.Throw<int>(new InvalidOperationException())));
            
// Execute an action for each element, on error, and on completion
var result = sequence
    .Do(
        i => Console.Write($"{i}, "),
        ex => Console.WriteLine("Failed: " + ex.Message),
        () => Console.WriteLine("Completed"));
    
Console.WriteLine("Before 1");
try
{
    result.Consume();
}
catch (InvalidOperationException) {}
Console.WriteLine("After 1");

flag = true;
Console.WriteLine("Before 2");
result.Consume();
Console.WriteLine("After 2");

// This code produces the following output:
// Before 1
// 1, 2, 3, 4, Failed: Operation is not valid due to the current state of the object.
// After 1
// Before 2
// 1, 2, 3, 4, 5, Completed
// After 2

Exceptions

Type	Condition
ArgumentNullException	source, onNext onError, or onCompleted is null.