Method Defer

Defer<TResult>(Func<IEnumerable<TResult>>)

Creates an enumerable sequence based on an enumerable factory function.

Declaration

public static IEnumerable<TResult> Defer<TResult>(Func<IEnumerable<TResult>> enumerableFactory)

Parameters

Type	Name	Description
Func<IEnumerable<TResult>>	enumerableFactory	Enumerable factory function.

Returns

Type	Description
IEnumerable<TResult>	Sequence that will invoke the enumerable factory upon iteration.

Type Parameters

Name	Description
TResult	Result sequence element type.

Remarks

enumerableFactory is not run until the sequence returned by Defer<TResult>(Func<IEnumerable<TResult>>) is enumerated. At enumeration, enumerableFactory is executed and the sequence returned is enumerated in a streaming manner and values are returned similarly.

enumerableFactory is executed each time the sequence returned by Defer<TResult>(Func<IEnumerable<TResult>>) is enumerated.

Examples

The following code example demonstrates how to defer the execution of a method that returns an enumerable using Defer.

var count = 3;

// Use a function to create a sequence at execution time
var result = SuperEnumerable
    .Defer(() => Enumerable.Range(1, count));

Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");
    
// changing count changes the length of the sequence 
// returned by the function given to Defer
count = 5;

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

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

Exceptions

Type	Condition
ArgumentNullException	enumerableFactory is null.
ArgumentNullException	(Thrown lazily) The sequence source returned by enumerableFactory is null.