How to clear vim registers effectively?

Since that venerable answer on the mailing list, linked by @romainl, we have setreg('a', []) that clears the register.

Thus, the code could become:

let regs=split('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-"', '\zs')
for r in regs
  call setreg(r, [])
endfor