Method Using

Using<TSource, TResource>(Func<TResource>, Func<TResource, IEnumerable<TSource>>)

Generates a sequence that's dependent on a resource object whose lifetime is determined by the sequence usage duration.

Declaration

public static IEnumerable<TSource> Using<TSource, TResource>(Func<TResource> resourceFactory, Func<TResource, IEnumerable<TSource>> enumerableFactory) where TResource : IDisposable

Parameters

Type	Name	Description
Func<TResource>	resourceFactory	Resource factory function.
Func<TResource, IEnumerable<TSource>>	enumerableFactory	Enumerable factory function, having access to the obtained resource.

Returns

Type	Description
IEnumerable<TSource>	Sequence whose use controls the lifetime of the associated obtained resource.

Type Parameters

Name	Description
TSource	Source element type.
TResource	Resource type.

Remarks

resourceFactory and enumerableFactory are evaluated lazily, once enumeration has begun. The value returned by resourceFactory will be disposed after the enumeration has completed.

The values returned by enumerableFactory and enumerableFactory are not cached; multiple iterations of the IEnumerable<T> returned by this method will call these methods separately for each iteration.

Examples

The following code example demonstrates how to create a sequence that throws on enumeration using Using.

var sequence = Enumerable.Range(1, 10);

// Hold a resource for the duration of an enumeration
var result = SuperEnumerable
    .Using(
        () => new DummyDisposable(),
        d => d.GetValues())
    .Do(x => Console.Write($"{x}, "));

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

// This code produces the following output:
// Constructor
// GetValues
// 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 
// Dispose
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

class DummyDisposable : IDisposable
{
    public DummyDisposable()
    {
        Console.WriteLine("Constructor");
    }

    public IEnumerable<int> GetValues()
    {
        Console.WriteLine("GetValues");
        return Enumerable.Range(1, 10);
    }
    
    public void Dispose()
    {
        Console.WriteLine();
        Console.WriteLine("Dispose");
    }
}

Exceptions

Type	Condition
ArgumentNullException	resourceFactory or enumerableFactory is null.