Can't understand the application of delegates in toString() functions

[Heisenberg via Digitalmars-d-learn]

On Monday, 7 November 2016 at 16:54:06 UTC, Ali Çehreli wrote:
> On 11/07/2016 08:40 AM, Heisenberg wrote:
>> [...]
>
> Exactly how it happens requires explaining a long chain of 
> function calls. Probably that's why the author did not 
> elaborate further. ;) I've probably omitted some steps here but 
> I think the following is close enough:
>
> - writeln() that's in the sample code calls write() with the 
> addition of '\n'.
>
> - write() eventually calls formattedWrite() with a 
> lockingTextWriter as the writer:
>
>   https://github.com/dlang/phobos/blob/master/std/stdio.d#L1401
>
> - formattedWrite() calls formatValue():
>
>   https://github.com/dlang/phobos/blob/master/std/format.d#L2906
>
> - formatValue() calls formatObject() and that's the one that 
> makes a distinction between different overloads of toString():
>
>   https://github.com/dlang/phobos/blob/master/std/format.d#L2805
>
> - formatObject() calls put(), which finally uses the 'sink' 
> parameter as an output range and fills in with characters.
>
> Ali

I see now. :) Sounds like I have to finish the whole book to be 
able to grasp all of that a little better. I think I do get a 
general picture now, though. Thanks for a quick reply, everyone!