This was intentionally removed by @Campbell Barton (campbellbarton) when not using the Emulate 3 Button Mouse feature.

The main motivation for adding the double-click feature, was that many users who are on laptops or tablets, or even many mice where it's uncomfortable to use the MMB, they use Emulate 3 Button Mouse which blocks the Alt key, making loop selections impossible. The ability to double-click got around this.

However, I believe there was some corner case or something where double-click could potentially interfere, so it was disabled unless the above feature is enabled.

(As an aside, Emulate 3 Button Mouse could become default perhaps, considering the variety and number of devices where MMB is either not available or uncomfortable, which would also reinstate double-click as a default behaviour)

That's very unfortunate. This was truly a handy feature and standard in most 3D apps. I don't think it's good to have it only for the Emulate 3 Button Mouse feature.
I hope you guys decide to bring that back.

In T58963#573021, @William Reynish (billreynish) wrote:

However, I believe there was some corner case or something where double-click could potentially interfere, so it was disabled unless the above feature is enabled.

I wouldn't call 'Selection Cycling' a corner case - This cycles between different elements under the pointer when 'limit select to visible' is enabled (xray in 2.8x).
It was broken by this feature, and not potentially - always (unless you purposefully clicked slowly so as not to trigger a double click event).

This works in object mode, pose mode, armature edit-mode etc. But edit-mesh wasn't working because of this key binding.

If you propose to remove selection cycling, thats a different matter - otherwise, modifications to key bindings shouldn't break existing functionality.

Sorry, but what is "selection cycling"?
Is it a very often used feature?
I can say that the double click to loop select made a lot of users happy. If there's a chance to bring this back, I'd go for it.

@ThinkingPolygons (ThinkingPolygons) if you have two or more objects under the mouse cursor, selecting them without moving the cursor cycles between those objects (or pose bones, edges... etc).

@Campbell Barton (campbellbarton) Okay I see. Most 3d softwares have this feature yeah, but usually only for object modes or similar. I never saw this in an edit mesh situation. I'm not even sure if it's that useful in edit mode.
Double click to loop select seems far more handy than this in edit mode tho.
But even in those other apps, this feature always requires you to "click slowly" for it to work, otherwise you'll trigger the double click event.
So I guess both features can still be available in edit mode without conflicting?

Ok, I just configured my keymap and did a quick test, and yes, both features are working pretty well together. The click for "cycling" is not that slow either. I can comfortably click to cycle or double click to loop select. So there are no issues at all imo.

I thought the change was intentional, it felt really good to select loops by just double clicking it. Consider bringing it back? Because now, double clicking is not bound to anything in a mesh's edit mode.

Bringing it back please it's really annoying.

This prevents two features from working well.

• Selection cycling.
• Selecting all boundaries. With this shortcut as default, boundary selection would require quadruple-click.

You can customize your keymap if you find this convenient.

Why it is disabled without "Emulate 3 button mouse"? It's really handy, but I don't want to emulate 3 buttons...