.net - What is the IObservable.Subscribe(IObserver<T> observer) overload for? -

when writing .subscribe expressions find resharper has chosen following overload me, located in mscorlib, version=4.0.0.0:

namespace system {   public interface iobservable<out t>   {     idisposable subscribe(iobserver<t> observer);   } } 

this seems different overloads take action , it's coming mscorlib , not system.reactive.* expect of reactive stuff be.

what overload do? how should used? how iobserver<t> relate action? , why single overload in mscorlib?

to clear, isn't overload, that's core of rx really. other subscribe methods, , other operators matter, you're used extension methods call that.

if @ documentation or rx, you'll see creators viewed push-based side of linq. lot of things mirror image of see in linq. iobservable mirror of ienumerable, , iobserver mirror of ienumerator.

however, because push opposite of pull, rx versions opposite of pull-based counterpart:

• ienumerable defines 1 method produces ienumerator. iobservable defines 1 method takes in iobserver.
• if think of ienumerator.movenext() + ienumerator.current 1 operation, can return in 1 of 3 ways: next element returned, end of collection reached, or exception thrown. similarly, iobserver has handle 3 cases: next element (onnext), end of stream (oncompleted), or exception (onerror).

the more familiar 'overloads' of subscribe extension methods this:

public static idisposable subscribe<t>(this iobservable<t> source, action<t> onnext) {     return subscribe(onnext, e => {/*onerror */}, () => {/*oncompleted*/); }  public static idisposable subscribe<t>(this iobservable<t> source, action<t> onnext, action<exception> onerror, action oncompleted) {     source.subscribe(new anonymousobserver<t>(onnext, onerror, oncompleted)); }