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On 2018-04-07 05:34 PM, Albert Chan wrote:
On Apr 7, 2018, at 2:58 PM, Reinder Feenstra <> 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, PUC-Rio
print(2 << -1)
print(2 >> 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.

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