Re: simply question about syntatic sugar
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- Subject: Re: simply question about syntatic sugar
- From: Dirk Laurie <dirk.laurie@...>
- Date: Sun, 7 Jun 2015 19:03:29 +0200
2015年06月06日 23:33 GMT+02:00 Rodrigo Azevedo <rodrigoams@gmail.com>:
> Let v be a usardata with a unary method, then
>
> v:abs() is a syntatic sugar for v.abs(v)
> v:reduce() is a syntatic sugar for v.reduce(v)
>
> etc
>
> This notation is very unpleasant. There is a problem if this behaviour of
> function calls
>
> v:abs is a syntativ sugar for v.abs(v)
> v:reduce is a syntatic sugar for v.reduce(v)
>
> was valid?
You can exploit the metatable mechanism so that v.Abs means v.abs(v).
Example:
mt = {__index = function(v,name)
local method = type(name)=='string' and rawget(v,name:lower())
if method then return method(v) end
end}
function cabs(v) return math.sqrt(v.x^2+v.y^2) end
tbl = setmetatable( {x=3, y=4, abs=cabs},mt)
tbl.Abs --> 5.0