Linq: iterator pipelines

[alrz]

Right now, using linq causes the entire iterator chain to be rebuilt each time even though the shape of it remains the same.

This could be avoided using an API like the following to cache the pipeline instance beforehand.

var iterator = Enumerable.CreateIterator<int>(static s => s.Where(x => x % 2 == 0));

var result1 = iterator(list1);
var result2 = iterator(list2);

The lambda should be static as it only runs once to build the iterator instance.

To accommodate this, iterators could support a custom arg to be specified.

var iterator = Enumerable.CreateIterator<int, int>(static s => s.Where(t => t.Item1 % t.Item2 == 0));

var result1 = iterator(list1, 2);
var result2 = iterator(list2, 4);

I think internally this could reuse Iterator infrastructure to represent the pipeline instance. This could accompany an IIterator<T> interface to support custom operators.

[huoyaoyuan]

The shape is not always the same. It takes optimization based on the interface implementations of input.