Any way to create derived classes from Exception with canned messages?

[jfondren]

On Saturday, 31 July 2021 at 08:25:56 UTC, Jeremy T. Gibson wrote:
> Now, https://github.com/dlang/druntime/blob/master/src/object.d 
> clearly expresses that the constructors of Exception are @nogc. 
>  Therein lies the problem: there is no way to use the ~ 
> concatenation operator in a @nogc function.  At least at my 
> current level of understanding of D (versus my background in C# 
> where this is trivial), I can't think of any other way to pass 
> a pure/nogc pair of strings that won't trip up the safety 
> parameters.
>
> Just as a raw test case, I tried the following:
>
> https://run.dlang.io/is/VmCKwV
>

`annotation()` should also be nothrow as it's called by the 
nothrow constructor.

Option #1: https://run.dlang.io/is/OBNfxq

use a limited @nogc string formatter from dub, with an instance 
buffer.

Option #2: https://run.dlang.io/is/Osoiyd

for such a simple format, do it manually.

Option #3: NotYetImplemented()

require the caller to call a non- at nogc function which can build a 
string and then throw/return a constructed exception.