/++ dub.sdl:

    dependency "bc-string" version="~>1.2.1"

 +/

import bc.string.format : nogcFormatTo;

import std.exception : assumeUnique;

​

class MyException : Exception {

    char[1024] buffer;

​

@nogc pure nothrow:

​

    @trusted private string annotate(string msg) {

        const len = nogcFormatTo!"%s %s"(buffer, msg, this.annotation);

        return buffer[0 .. len].assumeUnique;

    }

​

@safe:

    string annotation() {

        return "(annot)";

    }

​

    this(string msg, string file = __FILE__, size_t line = __LINE__, Throwable nextInChain = null) {

        super(annotate(msg), file, line, nextInChain);

    }

​

    this(string msg, Throwable nextInChain, string file = __FILE__, size_t line = __LINE__) {

        super(msg, file, line, nextInChain);

    }

}

​

void main() {

    throw new MyException("hi");

}