import std.string : representation;

import std.exception : assumeUnique;

​

class MyException : Exception {

    ubyte[1024] buffer;

​

@nogc pure nothrow:

​

    @trusted private string annotate(string msg) {

        immutable a = msg.representation;

        immutable b = annotation().representation;

        assert(a.length + b.length + 1 < buffer.length);

        buffer[0 .. a.length] = a;

        buffer[a.length] = ' ';

        buffer[a.length+1 .. a.length+1+b.length] = b;

        return assumeUnique(cast(char[])buffer);

    }

​

@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");

}