Re: Numeric for loop with rationals

[Tim Hill <drtimhill@...>]

> On Jan 30, 2018, at 6:55 AM, Soni They/Them L. <fakedme@gmail.com> wrote:
> 
> Lua 5.3.4  Copyright (C) 1994-2017 Lua.org, PUC-Rio
> > meta = {__add=function(x, y) return setmetatable({i=x.i + y.i}, meta) end, __lt=function(x, y) return x.i < y.i end}
> > function one() return setmetatable({i=1}, meta) end
> > function two() return setmetatable({i=2}, meta) end
> > function ten() return setmetatable({i=10}, meta) end
> > for i=one(), two(), ten() do print(i) end
> stdin:1: 'for' limit must be a number
> stack traceback:
>     stdin:1: in main chunk
>     [C]: in ?
> > local i,j,k=one(), ten(), two() while i < j do print(i) i = i + k end
> table: 0x558de8c74080
> table: 0x558de8c74200
> table: 0x558de8c747b0
> table: 0x558de8c74890
> table: 0x558de8c74970
> > local i,j,k=one(), ten(), two() while i < j do print(i.i) i = i + k end
> 1
> 3
> 5
> 7
> 9
> 
> Rationals don't work. Only floats and ints do. This sucks.
> 


You are basically arguing that the numeric-for should switch from using raw types to instead check for metamethods (basically __add/__sub and __lt/__le). While I agree that, from a purist standpoint, you are right, I think you will find that the argument against this is performance related. The extra checks would degrade numeric-for performance when it was used for the far more common numeric type.

And of course you can always use the generic-for anyway, so why do you need this?

—Tim