> import std.stdio;
>
> void main()
> {
>     real[int] a;
>     a[0] += 100;
>     writeln(a);
> }

results (independed of the used compiler) in

> [0:100]

I was a little bit surprised, because a[0] += 100 should be the same as a[0] = a[0]+100, which leads to a range violation error. Furthermore, as we work with real, I'd expected the result to be NaN...

Is this a bug? I ask, because it would be quite convenient to use it the way it works now.

An alternative I found, would be to use object.update. But there I've to declare the 100 twice which results in code duplication:

> a.update(0,()=>100.0L,(ref real v)=>v+100.0L);

Hence, my best solution needs two lines:

> if (0 !in a) a[0] = 0;
> a[0] += 100;

What's your oppinion on this?

On 27.08.19 18:12, berni wrote:
>> import std.stdio;
>>
>> void main()
>> {
>>     real[int] a;
>>     a[0] += 100;
>>     writeln(a);
>> }
> 
> results (independed of the used compiler) in
> 
>> [0:100]
> 
> I was a little bit surprised, because a[0] += 100 should be the same as a[0] = a[0]+100, which leads to a range violation error. Furthermore, as we work with real, I'd expected the result to be NaN...
> 
> Is this a bug? I ask, because it would be quite convenient to use it the way it works now.

For what it's worth, it's in Bugzilla:
https://issues.dlang.org/show_bug.cgi?id=4463

On Tuesday, 27 August 2019 at 16:12:07 UTC, berni wrote:
> What's your oppinion on this?

As someone relatively new to programming in general and to D in particular, this behavior does, on the surface, seem inconsistent.  Good to see that a bug exists for this, per ag0aep6g.

I never understood why the intial value of floats, doubles and reals was NaN.

Samir

On Tuesday, 27 August 2019 at 16:45:53 UTC, Samir wrote:
> I never understood why the intial value of floats, doubles and reals was NaN.

That's for detecting uninitialised variables. If the result of a calculation is NaN, it's likely, that you forgot to initialise the variable.