Indexing access for Lists and Maps considered harmful?

[Jean Louis Ardoint]

You can also easily encounter this with prefix or postfix operators and 
autoboxing, like in:

Map<Integer,Integer> m;
...
m[i] = m[i++]++ = i++;

Jean-Louis



From:
Bruce Chapman <brucechapman at paradise.net.nz>
To:
coin-dev <coin-dev at openjdk.java.net>
Date:
23/06/2009 12:04
Subject:
Re: Indexing access for Lists and Maps considered harmful?
Sent by:
coin-dev-bounces at openjdk.java.net



Talden wrote:
>> ...  We can have that if the construct is defined by
>> translation as:
>>
>> var tmp = "c";
>> map.put("b", tmp);
>> tmp
>> 
>
> This is my preference too...
>
> m[a] = n[a] = x; // where m and n are maps.
>
> becomes
>
> X t = x;
> m.put(a, t); n.put(a, t);
> t;
> 

Not quite!  because assignment is right associative - therfore

m[a] = n[a] = x; 


happens in the same order as

m[a] = (n[a] = x);

and therefore your translation should be

becomes

X t = x;
n.put(a, t);
m.put(a, t); 
t;

The difference could be detected for example when n and m were both 
references to the same LinkedHashMap and the keys were different therefore 
the order of iteration would reflect the order of assignment.

Bruce 



> Does semantically treating all multi-assignments this way break existing 
code?
>
> a = b = c;
>
> C t = c;
> a = t; b = t;
> t;
>
> Are there ways to get other side-effects in the current grammar? If
> not, defining it this way makes defining it for indexed access easier.
>
> PS: I've thought about this just long enough to write this email, it's
> one of those days... I must have missed something that makes this a
> more complex discussion other than 'this is how we should define the
> value of an indexed access expression'.
>
> --
> Talden
>
> 






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