some missions, you can choose what to put in your weapon some don't, and i don't find a create with attchaments in editor, but it's work well (beside wihat make a gun silent is no the supressor, but ammo, and supressor)

Not sure if I'm understanding you correctly here, but with the current gear system, if you only see a weapon, you can take that and equip it. If you want attachments for it, you can take them from anywhere you can find them and put it on the weapon.

And if you're looking say, at a crate which contains the weapon you want, with attachments on it, the tooltip and icon of the weapon shows them attached, and you can also take this.

It seems a very logical system. And to simulate realism, since that is what the game does, it would break this element if you could just pick up a weapon without any attachments and just magically select what attachments you want and they'd pop out of blue air.

I believe there's a loadout mod for the Alpha, and though I haven't tested it yet, I believe the one for Arma 2 allowed you to atleast save a loadout, and then select it even if you were nowhere near the items the loadout consisted of. That might be something you could look into as well

You can put whatever you want on whatever weapon you want, given it has a RIS.
The only attachment that you can't remove without changing the whole weapon are the bypod and the grenade launcher

The description of this ticket does not sufficiently convey any problem. Since it has been abandoned for a long time, I'm assuming the issue is obsolete.