Re: Who is using modified Lua versions, what are they and why?

On 27/06/2026 10:54, 'Sewbacca' via lua-l wrote:
> ... 
> So out of curiosity: Who is using modified Lua versions, what are the 
> modifications and why do you need them?

I use a patch to add an extra metamethod '__eqval', which is called when 
only one of the operands to the compare-equal operator (==) is a table 
or userdata; if both operands are tables or both are userdata then only 
the '__eq' metamethod is called as usual. The overhead on 'normal' 
equality comparisons is minimal or zero.

This allows a library which implements a higher level data type (let's 
call it T) as a table or userdata to be used more naturally when 
comparing directly with a number or a string. For example, if p is a 
variable holding a value of type T, you can write 'p == 2' and the 
__eqval metamethod will be called (unless p is just a number too). 
Otherwise you would have to write 'p == convert-to-T(2)'. The same 
applies when comparing two variables, one of which may contain a T and 
the other a simple value (number, string or boolean).

I've used this metamethod in an infinite precision arithmetic library in 
pure lua. It allows code written in other languages (eg a crypto package 
written in C) to be imported into lua with minimal effort.

-a

[patch for 5.4 is on Lua Power Patches 
<http://lua-users.org/wiki/LuaPowerPatches>. If anyone is interested I 
will upload patches for later Lua versions]

> 
> ~ Sewbacca
> 
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