The toString() of BigInt is not handy to print bigintegers during debugging. I have had to create a function like:

const(char)[] bigIntRepr(BigInt i) {
    const(char)[] result;
    i.toString((const(char)[] s){ result = s; }, "d");
    return result;
}


Note that this doesn't work (Access violation, I don't know why):

const(char)[] bigIntRepr(BigInt i) {
    const(char)[] result;
    i.toString((const(char)[] s){ result = s; }, null);
    return result;
}


My suggestion is to change the signature of BigInt.toString() from this:

void toString(void delegate(const (char)[]) sink, string formatString) const {


To something like this:

string toString(void delegate(string) sink=null, string formatString="d") const {   

And make it return a string filled with the decimal representation when sink is null; and to return an empty string when sink!=null.

------------------------

Eventually the signature can even become:

string toString(void delegate(string) sink=null, string formatString="d", string thousands="") const {

So if thousands="_" the number gets represented as:

"100_000_000_000"

But this is less important.