How to declare immutable struct outside of try catch and reference it later

[kdevel]

On Sunday, 3 December 2017 at 23:29:01 UTC, Basile B. wrote:
> On Sunday, 3 December 2017 at 22:33:40 UTC, kdevel wrote:
>> On Sunday, 3 December 2017 at 14:58:03 UTC, Basile B. wrote:
>>> In this case i'd go for a typed pointer, e.g
>>>
>>> ---
>>> immutable struct Configuration
>>> {
>>>     this(string){/*load some file...*/}
>>>     int value;
>>> }
>>>
>>> Configuration* config;
>>>
>>> void main()
>>> {
>>>     try config = new Configuration("config.sdl");
>>>     catch(Exception){}
>>>     // config.value = 42; // ok, read only
>>> }
>>> ---
>>
>> When config is null, e.g. in case "load some file..." threw, 
>> you get a segfault. No error handling at all!
>
> I don't follow you...the file thing happens in the __ctor. 
> Exceptions are well handled.

But not in the code you provided first. You used to ignore the 
exception:

    catch(Exception){}

> Maybe you've missed the try (w/o braces) ?

Not really.

> ---
> immutable struct Configuration {
>     this(string){/*parse_config...*/}
> }
>
> Configuration* config;
>
> int main() {
>     try {
>         config = new Configuration("config.sdl");
>         // instead of "conf = parse_config("config.sdl");"
>     } catch(Exception e){
>         std.stdio.stderr.writeln("Error reading configuration 
> file: ", e.msg);
>         return 1;
>     }
> }
> ---

Are my eyes too weak or is my compiler too old? For this piece of 
code

test.d
```
immutable struct C {
    this (string filename)
    {
    }
}

void main ()
{
    auto config = new C ("config.sdl");
}
```

it says: test.d(9): Error: immutable method test.C.this is not 
callable using a mutable object

→ https://issues.dlang.org/show_bug.cgi?id=13628
→ 
http://forum.dlang.org/thread/mailman.926.1413747186.9932.digitalmars-d-bugs@puremagic.com