Method Catch

Catch<TSource, TException>(IEnumerable<TSource>, Func<TException, IEnumerable<TSource>>)

Creates a sequence that corresponds to the source sequence, concatenating it with the sequence resulting from calling an exception handler function in case of an error.

Declaration

public static IEnumerable<TSource> Catch<TSource, TException>(this IEnumerable<TSource> source, Func<TException, IEnumerable<TSource>> handler) where TException : Exception

Parameters

Type	Name	Description
IEnumerable<TSource>	source	Source sequence.
Func<TException, IEnumerable<TSource>>	handler	Handler to invoke when an exception of the specified type occurs.

Returns

Type	Description
IEnumerable<TSource>	Source sequence, concatenated with an exception handler result sequence in case of an error.

Type Parameters

Name	Description
TSource	Source sequence element type.
TException	Exception type to catch.

Remarks

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to use the Catch operator.

// this sequence will throw an exception on the 6th element
var sequence = Enumerable.Range(1, 5).Select(i => i.ToString())
    .Concat(SuperEnumerable.Throw<string>(new InvalidOperationException()));

// Use a function to determine how to handle an exception
var result = sequence
    .Catch(
        (InvalidOperationException ex) => SuperEnumerable.Return(ex.Message));

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

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

Exceptions

Type	Condition
ArgumentNullException	source or handler is null.
ArgumentNullException	(Thrown lazily) The sequence errSource returned by handler is null.

Catch<TSource>(IEnumerable<TSource>, IEnumerable<TSource>)

Creates a sequence that returns the elements of the first sequence, switching to the second in case of an error.

Declaration

public static IEnumerable<TSource> Catch<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)

Parameters

Type	Name	Description
IEnumerable<TSource>	first	First sequence.
IEnumerable<TSource>	second	Second sequence, concatenated to the result in case the first sequence completes exceptionally.

Returns

Type	Description
IEnumerable<TSource>	The first sequence, followed by the second sequence in case an error is produced.

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 use the Catch operator.

// this sequence will throw an exception on the 6th element
var sequence = Enumerable.Range(1, 5)
    .Concat(SuperEnumerable.Throw<int>(new InvalidOperationException()));

// Use a second sequence to continue in the case of an exception
var result = sequence
    .Catch(Enumerable.Range(1, 5));

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

// This code produces the following output:
// [1, 2, 3, 4, 5, 1, 2, 3, 4, 5]

Exceptions

Type	Condition
ArgumentNullException	first or second is null.

Catch<TSource>(params IEnumerable<TSource>[])

Creates a sequence by concatenating source sequences until a source sequence completes successfully.

Declaration

public static IEnumerable<TSource> Catch<TSource>(params IEnumerable<TSource>[] sources)

Parameters

Type	Name	Description
IEnumerable<TSource>[]	sources	Source sequences.

Returns

Type	Description
IEnumerable<TSource>	Sequence that continues to concatenate source sequences while errors occur.

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 use the Catch operator.

// this sequence will throw an exception on the 6th element
var sequence = Enumerable.Range(1, 5)
    .Concat(SuperEnumerable.Throw<int>(new InvalidOperationException()));

// Use a series of sequences to enumerate until one completes successfully.
var result = SuperEnumerable
    .Catch(
        sequence, 
        sequence,
        Enumerable.Range(1, 3), 
        Enumerable.Range(1, 10));

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

// This code produces the following output:
// [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3]

Exceptions

Type	Condition
ArgumentNullException	sources is null.
ArgumentNullException	(Thrown lazily) Any sequence source returned by sources is null.

Catch<TSource>(IEnumerable<IEnumerable<TSource>>)

Creates a sequence by concatenating source sequences until a source sequence completes successfully.

Declaration

public static IEnumerable<TSource> Catch<TSource>(this IEnumerable<IEnumerable<TSource>> sources)

Parameters

Type	Name	Description
IEnumerable<IEnumerable<TSource>>	sources	Source sequences.

Returns

Type	Description
IEnumerable<TSource>	Sequence that continues to concatenate source sequences while errors occur.

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 use the Catch operator.

// this sequence will throw an exception on the 6th element
var sequence = Enumerable.Range(1, 5)
    .Concat(SuperEnumerable.Throw<int>(new InvalidOperationException()));

// Use a series of sequences to enumerate until one completes successfully.
var result = SuperEnumerable
    .Catch(
        new List<IEnumerable<int>>
        {
            sequence,
            sequence,
            Enumerable.Range(1, 3),
            Enumerable.Range(1, 10),
        });

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

// This code produces the following output:
// [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3]

Exceptions

Type	Condition
ArgumentNullException	sources is null.
ArgumentNullException	(Thrown lazily) Any sequence source returned by sources is null.