• berni (11/22) Aug 27 2019 I was a little bit surprised, because a[0] += 100 should be the
• ag0aep6g (3/22) Aug 27 2019 For what it's worth, it's in Bugzilla:
• Samir (8/9) Aug 27 2019 As someone relatively new to programming in general and to D in
• berni (4/6) Aug 27 2019 That's for detecting uninitialised variables. If the result of a

berni <someone somewhere.com> writes:

 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?

ag0aep6g <anonymous example.com> writes:

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

Samir <samir aol.com> writes:

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

berni <someone somewhere.com> writes:

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.