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digitalmars.D.learn - Unexplainable behaviour with direct struct assignment.

reply HuskyNator <HuskyNator protonmail.ch> writes:
I came across strange, seemingly non-deterministic, behaviour 
today. I simplified it the best I could below. I entice you to 
run the following piece of code.

```d
module app;
import std.stdio;

struct A {
	float[1] vec;
	this(float[1] n) {
		this.vec = n;
	}
}

void main(string[] args) {
	A c = A([50.0f]);
	writeln(c.vec[0]);

	A b = A([50.0f]);
	writeln(b.vec[0]);

	c = A([50.0f]);
	writeln(c.vec[0]);
}
```

This will print:
```
0
50
nan
```

My findings:
- The first initializer will always contain 0
- Initialization to another variable will yield the expected 50
- Reinitialization will always yield null

Am I missing something? Is this a bug? I have no idea what is 
wrong.
Thanks for you help,
- HN
May 18 2022
next sibling parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Wed, May 18, 2022 at 08:05:05PM +0000, HuskyNator via Digitalmars-d-learn
wrote:
[...]

 ```d
 module app;
 import std.stdio;
 
 struct A {
 	float[1] vec;
 	this(float[1] n) {
 		this.vec = n;
 	}
 }
 
 void main(string[] args) {
 	A c = A([50.0f]);
 	writeln(c.vec[0]);
 
 	A b = A([50.0f]);
 	writeln(b.vec[0]);
 
 	c = A([50.0f]);
 	writeln(c.vec[0]);
 }
 ```
 
 This will print:
 ```
 0
 50
 nan
 ```


[...]

Can't replicate this problem. On my local machine (Linux/64), I get the
output:

````
50
50
50
````

What's the exact compile command you're using?


T

-- 
To err is human; to forgive is not our policy. -- Samuel Adler
May 18 2022
prev sibling parent reply Dennis <dkorpel gmail.com> writes:
On Wednesday, 18 May 2022 at 20:05:05 UTC, HuskyNator wrote:

 This will print:
 ```
 0
 50
 nan
 ```


Which compiler and flags are you using? For me it just prints 50, 
you might be stumbling on some (old) bugs in the DMD backend with 
floating point registers. Examples of such bugs are:

https://issues.dlang.org/show_bug.cgi?id=18573
https://issues.dlang.org/show_bug.cgi?id=22163
May 18 2022
parent reply HuskyNator <HuskyNator protonmail.ch> writes:
On Wednesday, 18 May 2022 at 20:16:51 UTC, Dennis wrote:

 On Wednesday, 18 May 2022 at 20:05:05 UTC, HuskyNator wrote:

 This will print:
 ```
 0
 50
 nan
 ```


 Which compiler and flags are you using? For me it just prints 
 50, you might be stumbling on some (old) bugs in the DMD 
 backend with floating point registers. Examples of such bugs 
 are:

 https://issues.dlang.org/show_bug.cgi?id=18573
 https://issues.dlang.org/show_bug.cgi?id=22163


I've been using `DMD 2.098.0` using a default DUB (1.27.0) init 
project (I'm not quite sure what the compile flags are).

After updating to `DMD 2.100.0` & `DUB 1.29.0`, I still get this 
behavior.
Only when I use `dub run --b=debug` however (default for me). 
`dub run --b=release` does return what one would expect.
May 18 2022
next sibling parent reply HuskyNator <HuskyNator protonmail.ch> writes:
On Wednesday, 18 May 2022 at 21:49:14 UTC, HuskyNator wrote:

 After updating to `DMD 2.100.0` & `DUB 1.29.0`, I still get 
 this behavior.
 Only when I use `dub run --b=debug` however (default for me). 
 `dub run --b=release` does return what one would expect.


I don't know if this matters either, but I'm using windows 10 (64 
bits).
May 18 2022
next sibling parent reply Tejas <notrealemail gmail.com> writes:
On Wednesday, 18 May 2022 at 21:52:18 UTC, HuskyNator wrote:

 On Wednesday, 18 May 2022 at 21:49:14 UTC, HuskyNator wrote:

 After updating to `DMD 2.100.0` & `DUB 1.29.0`, I still get 
 this behavior.
 Only when I use `dub run --b=debug` however (default for me). 
 `dub run --b=release` does return what one would expect.


 I don't know if this matters either, but I'm using windows 10 
 (64 bits).


Does this happen with LDC as well?
May 18 2022
parent HuskyNator <HuskyNator protonmail.ch> writes:
On Thursday, 19 May 2022 at 04:33:01 UTC, Tejas wrote:

 Does this happen with LDC as well?


I tried it using `LDC 1.29.0` and it prints correctly under both 
`--b=release` and `--b=debug` builds.
May 19 2022
prev sibling parent bauss <jj_1337 live.dk> writes:
On Wednesday, 18 May 2022 at 21:52:18 UTC, HuskyNator wrote:

 On Wednesday, 18 May 2022 at 21:49:14 UTC, HuskyNator wrote:

 After updating to `DMD 2.100.0` & `DUB 1.29.0`, I still get 
 this behavior.
 Only when I use `dub run --b=debug` however (default for me). 
 `dub run --b=release` does return what one would expect.


 I don't know if this matters either, but I'm using windows 10 
 (64 bits).


Can confirm this is the case for me too on Windows 10.

Release prints 50 3 times, debug prints 0, 50, nan.

This is with DMD, I currently don't have LDC or GDC installed on 
this machine.

So it looks like a Windows bug, critical at that.
May 18 2022
prev sibling parent frame <frame86 live.com> writes:
On Wednesday, 18 May 2022 at 21:49:14 UTC, HuskyNator wrote:


 After updating to `DMD 2.100.0` & `DUB 1.29.0`, I still get 
 this behavior.
 Only when I use `dub run --b=debug` however (default for me). 
 `dub run --b=release` does return what one would expect.


I'm still on 2098.1, Windows 10 and get this at 64bit only

```
9.18366e-40
50
nan
```

but no matter if debug build or not.
May 19 2022