Re: Arithmetic on strings

[Peng Zhicheng <pengzhicheng1986@...>]

于 2012-6-13 19:21, Dirk Laurie 写道:
> It seems to be impossible to override arithmetic operators on
> strings.  One can for example set the __add metamethod, but
> it only gets called when at least one of the strings cannot be
> coerced to a number.  For example:
>
>     getmetatable''.__add = function(x,y) return x..y end
>     'a'+'b' -->  'ab', fine
>     '1'+'2' -->  3

No, you can't do such in Lua.

Lua would automatically call tonumber on strings when doing arithmetic operation.
and the same applied to concat operation on numbers.

i.e.

"3" + "4"      =>  7
3  .. 4        =>  "34"  (note the space between number and ..)