First project: questions on how-to, and on language features

[Alex Vincent via Digitalmars-d-learn]

Source code:
https://alexvincent.us/d-language/samples/intervalmap-rev1.d.txt

After reading Ali Çehreli's book, "Programming in D", I wrote 
this little sample up as a starting point for my explorations 
into D.  I've long admired the D language, but I've never 
actually tried to write practical code in D.

So I wrote this little sample up in dlangide, and as I was going, 
I realized I had quite a few questions.

(1) It's not clear how to specify certain parts of a module or 
library as non-exportable.  Is that possible?  Is it desirable?  
(It's not that important, yet, but still...)

(2) In the unittest code, I have a block that I want to rewrite 
using assertThrown, but I can't figure out from either the book 
or the website the correct usage.  What's the right way to 
specify a StringException with a particular message I expect to 
receive?

(3) How do I actually create a library in dub?  How does dub 
determine what files to build?

(4) How should the scope(exit) and scope(failure) guard 
statements intermix with preconditions and postconditions?

(5) My append() function has a postcondition that currently 
depends on debug-only members of the class being set in the 
precondition.  This seems artificial - not the part about setting 
these variables in the precondition, but having the variables 
defined on the class to begin with.  If they were defined only 
for the lifetime of the function's execution, starting in the 
precondition, this would be more natural.  Is there a Right Way 
to define function-only debug variables for use in 
postconditions?  If not, would this be a valid use-case to 
consider amending the language specification to clarify?

(6) Would someone please review my sample code and offer 
feedback?  :-)

(7) Naming:  This code is the start of a port of a mini-library I 
wrote in JavaScript which I called "ObjectRange".  However, in 
Phobos, the term "Range" has a very different meaning - in fact, 
almost the opposite meaning of what this code does.  I asked for 
a better name in the D IRC channel, and someone suggested 
Interval, based on the mathematical definition of the word.  
IntervalMap seemed more accurate, since there is a payload to 
each interval.  Does the name make sense in the context?

(8) Is there a similar, more mature library out there which tries 
to achieve what I'm doing here?  I'm rather surprised I didn't 
see anything like it in the standard library...