Can you use a longbow in melee to get Great Weapon Master and Sharpshooter in a single attack for +20 damage?

@JeremyECrawford Can you use a longbow in melee to get GWM and Sharpshooter in a single attack for +20 damage?

— Rystefn (@Rystefn) November 22, 2017

If you use a weapon in a way that turns it into an improvised weapon—such as smacking someone with a bow—that weapon has none of its regular properties, unless the DM rules otherwise. #DnD https://t.co/1gOFFT764D

— Jeremy Crawford (@JeremyECrawford) November 22, 2017