Re: inconsistencies between arithmetic and boolean operators

[Adrien de Croy <adrien@...>]

actually you'd need to put STRING below NUMBER, else

1 > "Fish"

if we converted the rhs to a number would return true, as "Fish" would 
convert to 0. whereas

1 > "Fish"

if we converted the lhs to a string would return false on the string 
compare since "1" < "Fish" using lstrcmp.

In the end, probably best to just convert anything to a string if they 
aren't the same type then do the comparison.

e.g.


int lua_CheckTypes(lua_State* L, TValue *lhs, TValue *rhs)
{
   int nLhsType = ttype(lhs);
   int nRhsType = ttype(rhs);
   const TValue* tmL;
   const TValue* tmR;
   if(nLhsType == nRhsType)
      return 1;

   // just do all comparisons as string.
   return (tostring(L, lhs) && tostring(L, rhs));
}


then in code where we call

   if(ttype(lhs) == ttype(rhs))

we replace that with

   if(lua_CheckTypes(L, lhs, rhs))



Adrien


Adrien de Croy wrote:
> As work on __cast progresses, I've come across an issue relating to 
> boolean operators.
>
> Arithmetic operators attempt to convert both operands to a number 
> first, so they work fine with __cast.
>
> boolean operators insist however that the 2 operands have the same 
> type, else the result is zero.  This is checked first.
>
> This means that the following code
>
> var1 = "3";
> var2 = var1 * 2;
>
> is valid and var2 will have the numeric value of 6
>
> however
>
> var1 = "3"
> if(var1 < 4) then
> ...
>
> is invalid, since var1 and 4 have different types, the result is an 
> error.  If you wanted this to "work" you'd need to write
>
> var1 = "3"
> if((var1 * 1) < 4) then
> ...
>
> the multiplication converts var1 in-place to a number.
>
> Shouldn't the boolean operators try and do something like this?
>
> e.g. instead of simply returning false on a type mismatch, try (e.g. 
> by __cast metamethod) to demote the higher type to the lower type, 
> where the precedence of types is (in descending order)
>
> TABLE
> USERVALUE
> STRING
> NUMBER
> BOOLEAN
>
>
> Adrien

--
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