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From Jochen Theodorou <blackd...@gmx.org>
Subject Re: New syntax explosion
Date Thu, 05 Oct 2017 23:12:51 GMT
On 06.10.2017 00:06, Jesper Steen Møller wrote:
> Hi List
> 
>> On 5 Oct 2017, at 20.01, eric.milles@thomsonreuters.com 
>> <mailto:eric.milles@thomsonreuters.com> wrote:
>>
>> [...]
>> `a??.b.c.` is just `a?.b?.c`
> 
> Are there any cases where a?.b.c would every make sense -- if a is null, 
> then the expression would throw anyway, wouldn't it? Or is there some 
> dynamic mixin case I'm not taking into consideration?
> 
> In other words, IMHO a?.b.c should implicitly mean a?.b?.c or at least 
> give a warning that the construct doesn't make sense. In either case ??. 
> wouldn't make much sense.

I personally think we made a mistake with ?. Instead of safe navigation, 
we should stop evaluation

x = a?.b?.c?.d

is translated as:

var tmp
tmp = a==null?null: a.b
tmp = tmp==null?null: tmp.c
tmp = tmp==null?null: tmp.d
x = tmp

and x = a?.b.c.d is

var tmp
tmp = a==null?null: a.b
x = tmp.c.d

while x = a??.b.c.d is

var tmp
tmp = a==null?null: a.b.c.d
x = tmp

As you can see the constructs a??.b.c.d and a?.b?.c?.d can have 
different implementations.

I would favor replacing ?. with what ??. does. I doubt it would really 
break any programs.

> As for the other constructs, I'm also not a big fan of introducing lots 
> of new syntax just because we can.
> There is a collateral cost to pay, e.g. in the type checker and static 
> compiler (within the Groovy project's control), too, and in every AST 
> transformer which needs to know about the new stuff (out of the 
> Groovyproject's control!) .

well, that is where the current version shines... They are parse time 
constructs, no new AST required, no new compilation required (only for 
optimization), no new checks required.

But I would go further... just because the collateral cost is low, does 
not make the construct more appealing. For syntax, semantics and 
use-case have to decide.

bye Jochen


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