A base class for objects that can be queried at runtime for extra features.
class type t = object ... endprobe t feature checks whether t supports feature. This is mostly for internal use. For example, Eio_unix.FD.peek_opt uses this to get the underlying Unix file descriptor from a flow.
Resources are usually attached to switches and closed automatically when the switch finishes. However, it can be useful to close them sooner in some cases.
class type close = object ... endval close : close -> unitclose t marks the resource as closed. It can no longer be used after this.
If t is already closed then this does nothing (it does not raise an exception).
Note: if an operation is currently in progress when this is called then it is not necessarily cancelled, and any underlying OS resource (such as a file descriptor) might not be closed immediately if other operations are using it. Closing a resource only prevents new operations from starting.