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From Jochen Theodorou <blackd...@gmx.org>
Subject Re: [PROPOSAL]new operator ?=
Date Wed, 23 Nov 2016 09:36:39 GMT


On 23.11.2016 09:34, Marcin Erdmann wrote:
[...]
> I will chip in as the person who proposed that new operator on Twitter to
> Daniel (thanks Daniel and Guillaume for raising it for discussion here).
> This idea came up when I needed to add a default key in a map pre-populated
> with another map:
>
>     def options = [:]
>     options.putAll(userOptions)
>     options.fit = options.fit ?: "max"

well, you could have done this:

def options = [ fit : "max" ]
options.putAll(userOptions)

then there is no show time for elvis

> I think that from the above you can see that this operator makes more sense
> when you are defaulting a value that is nested and not just a local
> variable. To make it even more drastic:
>
>     foo.options.fit = foo.options.fit ?: "max"
>
> vs.
>
>     foo.options.fit ?= "max"

or Cedric's variant:

foo.options.with {
   fit ?= "max" //fit = fit ?: "max"
}

Maybe my problem stems more from me not really being happy with ?= as 
symbol group. For a ?: b being the short form of a? a : b is pretty 
straightforward. Having a reduction of the reduction... well that's 
where you can easily loose context. It is then not so easy anymore that 
a ?= b is the short form of a = a ? a : b... especially since this is a 
pretty special case with rare usages. And going by the usually pattern 
this really would have to be a ?:= b, which is just too much ASCII-art 
for some here.

I mean something like a += b is kind of special too, but it is also many 
times more common than ?=, because calculations are a much more common 
case than after-the-fact-initialization

[...]
> Anyway, I see that it looks like Daniel has decided that it's not worth the
> effort but thanks to everybody for taking my proposal into consideration.

Maybe we should start a vote of ?= or not... maybe on the user list... 
then we see what people think. Daniel might have been a bit too fast here

bye Jochen

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