Method Memoize

Memoize<TSource>(IEnumerable<TSource>, bool)

Creates a sequence that lazily caches the source as it is iterated for the first time, reusing the cache thereafter for future re-iterations. By default, all sequences are cached, whether they are instantiated or lazy.

Declaration

public static IBuffer<TSource> Memoize<TSource>(this IEnumerable<TSource> source, bool forceCache = true)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
bool	forceCache	Force caching of ICollection<T>s.

Returns

Type	Description
IBuffer<TSource>	Returns a sequence that corresponds to a cached version of the input sequence.

Type Parameters

Name	Description
TSource	Type of elements in source.

Remarks

The returned IEnumerable<T> will cache items from source in a thread-safe manner. The sequence supplied in source is not expected to be thread-safe but it is required to be thread-agnostic. The iterator returned by GetEnumerator() is not thread-safe, and access should be limited to a single thread/task or controlled via external locks.

By default, Memoize<TSource>(IEnumerable<TSource>, bool) will choose the safe option and cache all IEnumerable<T>s. ICollection<T> will use an optimized form using CopyTo(T[], int), while other IEnumerable<T>s will cache iteratively as each element is requested.

However, if forceCache is set to false, then data in an ICollection<T> will be returned directly and not cached. In most cases, this is safe, but if the collection is modified in between uses, then different data may be returned for each iteration.

Examples

The following code example demonstrates how to cache a sequence for repeated use using Memoize.

var count = 0;
var sequence = Enumerable.Range(1, 10)
    .Do(_ => count++);

// get leading elements
var result = sequence.Memoize();

Console.WriteLine($"iterations: {count}");
Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");
Console.WriteLine($"iterations: {count}");
Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");
Console.WriteLine($"iterations: {count}");

// This code produces the following output:
// iterations: 0
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
// iterations: 10
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
// iterations: 10

Exceptions

Type	Condition
ArgumentNullException	source is null.