Re: Long chains of objects (aka tables)

[Andrew Starks <andrew.starks@...>]

On Saturday, May 17, 2014, Thiago L. <fakedme@gmail.com> wrote:
> On 17/05/2014 13:54, Jay Carlson wrote:
> > On May 16, 2014, at 6:45 PM, Thiago L. <fakedme@gmail.com> wrote:
> >
> > > So I did some benchmarking: https://gist.github.com/SoniEx2/4b1d9d8e6427cf5a1439
> > >
> > > It seems like pcall is almost the best way to do Groovy's ?. stuff in Lua: http://groovy.codehaus.org/Null+Object+Pattern
> > > (let me quote it)
> > > "with the |?.| operator, an _expression_ like |p?.job?.salary| will be equal to null if |salary| is equal to null, or if |job| is equal to null or if |p| is equal to null. You don't need to code a complex nested |if ... then ... else| to avoid a |NullPointerException|."
> > >
> > > (actually pcall is more like catching a NullPointerException but w/e)
> > If you can stand doing this at statement context, you could macro-transform
> >
> >      local v ?= t.t1.t2.t3
> >
> > into either
> >
> >      local v = t and
> >        t.t1 and
> >        t.t1.t2 and
> >        t.t1.t2.t3
> >
> > or
> >
> >      local v = t
> >      v = v and v.t1
> >      v = v and v.t2
> >      v = v and v.t3
> >
> > In the case of the (unrealistic) nesting level of that gist, the latter seems about ten times faster. At a depth of 4 it's only ~2.5 times faster.
> >
> > If there were a way to change the definition of "." inside a lexical scope, that might be interesting. Going after nil's metatable will break code outside the consenting scope.
> >
> > Jay
> I want something like |local v = t?t1?t2?t3|... (actually I want |local v = t?.t1?.t2?.t3|...)

I think that an important detail is that both selectors are important, sometimes in the same object. Usually a specific property group or mixin is optional, but not every branch on the tree is. 

Also, ? In an assignment should be error:

A?b = c

--error