On Wednesday, 25 August 2021 at 12:11:01 UTC, Johann Lermer wrote:
Hi all,
I have a little problem understanding alias this. I always
thought, that alias this only makes implicit conversions from
the aliased object to this. Then, why do lines 18 and 22
compile in the code below? And, btw, line 22 crashes with a
segmentation fault.
```d
01 struct Test_Struct {long t;}
02
03 class Alias_Class
04 {
05 Test_Struct ts;
06 alias ts this;
07 }
08
09 class Test_Class
10 {
11 Alias_Class ac;
12 }
13
14 void main ()
15 {
16 auto ac = new Alias_Class;
17 Test_Struct ts = ac; // compiles
18 ac = ts; // compiles as well - why?
19
20 auto tc = new Test_Class;
21 ts = tc.ac; // compiles
22 tc.ac = ts; // again this compiles, but seg
faults
23 }
```
Johann
ts is a field. You can assign to a field. So when the field is
aliased to this, you can assign to the field through a class
reference.
You can disable this behavior by creating a getter in
Alias_Class, then aliasing it to this:
```
class Alias_Class
{
Test_Struct ts;
Test_Struct getter() { return ts; }
alias getter this;
}
```
