Zitat von Marco Bungart <m.bung...@gmx.net>:
> Hi Michael,
>
Hi Marco,
> Am 16.10.2014 um 22:13 schrieb Michael Dietrich:
>> Hello,
>>
>> I'm getting started with X10 and am a bit stuck with the handling of
>> Rails (I think I might get the same problem with Arrays and so on).
>>
>> Let's say I create the following:
>>
>> val bla = new Rail[Long](10);
>> bla(0) = 2343;
>> bla(1) = 4534;
>> bla(2) = 3424;
>> for(i in 0..9)
>> bla(i)=42;
>> Console.OUT.print("Content: ");
>> Console.OUT.println(bla);
>>
>> I get 42 ten times as an output.
>> My first question: At least the first three values of my Rail are set.
>> As far as I understood "val" makes them become immutable. So why can I
>> turn them all into 42?
>
> The semantics are not like in C(++) (where the Array AND its entry are
> immutable), but only the reference to the array is immutable, like in
> Java. Meaning: you can modify single entries, but you cannot write
> bla = new Rail[Long] (...);
>
> after the first initialization.
>
>
Yes, I'm more familiar with C/C++ than with Java. ;)
>>
>> My second question: If I change the for-loop into
>>
>> for(b in bla)
>> b=42;
>>
>> I get the expected error message by the compiler though it's actually
>> no formal change. Or is there any?
>>
>> bye
>> Michael
>
> You should wirte the loop as
> for (b:Long in bla) { b = 42;}
>
> which results in this compiler-error:
> Final variable might already have been initialized.
> Final variable: b
>
> Writing
> for (var b:Long in bla) { b = 42; }
> Leads to:
> Enhanced for loop may not have var loop index. var b: Long{amb}
> Final variable might already have been initialized.
> Final variable: b
>
> In other words: if you use primitive data types (int, long, double,
> ...), you will not be able to change them with a foreach-loop. Even if
> you were able to change the value of b, you would change ONLY the value
> of b, since primitives are copied and not referenced.
> If, on the other hand, your Rail holds objects, the loop-variable (b)
> will hold references. While b is still a val, you would be able to
> change attributes of b (just like you were able to change entries in the
> Rail bla despite it being a val) and since b is only a reference to the
> object in the Rail, you would get the desired result.
>
Okay, thanks.
> I hope i was able to help. Feel free to ask further questions.
>
I think in the future there will be much more since I'm writing my
bachelors' thesis about high performance programming languages
including X10. ;-)
> Cheers,
> Marco
>
>
>
Bye
>>
>>
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>
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