Re: __bshr vs __bshl

["Soni \"They/Them\" L." <fakedme@...>]

On 2018-04-07 05:34 PM, Albert Chan wrote:
> > On Apr 7, 2018, at 2:58 PM, Reinder Feenstra <reinderfeenstra@gmail.com> wrote:
> >
> > Hi All,
> >
> > While implementing all meta methods in some glue code between Lua and
> > C++ I'd became curious why __bshr and __bshl both exist. For the
> > compare operators a smart trick is used so you don't need to implement
> > them all.
> >
> > To make sure my glue code behaves the same as Lua I simply tried all
> > operators, e.g.
> >
> > Lua 5.3.3  Copyright (C) 1994-2016 Lua.org, PUC-Rio
> > > print(2 << -1)
> > 1
> > > print(2 >> 1)
> > 1
> >
> > This is legal in Lua, so why not only a __bshr meta method and call
> > this with a negative shift count for the << operator?
> Same reason we have __sub operator (for convenience):
>
> A - B = A + (-B)
>
> A + (-B) is legal in Lua, so why not ...
Why have __add or __unm at all anyway

A + B == A - (0 - B)
-A == (0 - A)

Also why have __mul

A * B == A / (1 / B)

And so on.

--
Disclaimer: these emails may be made public at any given time, with or without reason. If you don't agree with this, DO NOT REPLY.