Re: Feature Request: rawset return value from __newindex

[Peng Zhicheng <pengzhicheng1986@...>]

于 2011年10月20日 08:12, Daurnimator 写道:
> A small feature request to distract you all from the noise on the list recently:
>
> I often find myself writing code like
> mt.__newindex = function ( t , k , v )
>      v = dosomethingwithv ( v )
>      rawset(t,k,v)
> end
>
> Could we make it so the return value of __newindex is then set as the
> value in t?
>
> It will be backwards compatible, as the majority of code out there
> don't return anything from __newindex operations.
>
> Benefits
>   - One less line of code
>   - __newindex operations can now do a tail call; `function (t,k,v)
> return dosomethingwithv(v) end;
>   -  I assume it can be optimised quite well in the actual
> implementation, as the key has already been hashed; and we know its
> not already in the table.
>
>
> Daurn.
the __newindex meta method, or event, is triggered when a non-existing field of one table is being set.
so the semantic type is an assignment *statement*, not an *expression*. so it is meaningless to return values.

so the __index event is to evaluate an expression, while __newindex is to execute a statement.