D at University of Minnesota

Carl Sturtivant sturtivant at gmail.com
Sat Aug 17 08:22:24 PDT 2013

>> What happened is that I unclear what the state of play is; I 
>> am not
>> asserting the wrongness of TDPL. Still, I am reassured by your 
>> responses.
> Hi Carl -- TDPL is for the most part in good shape. There are a 
> few inaccuracies, but I'd say most concern corner cases that 
> are unlike to deter the learning process.
> You may want to encourage students to interact with us here, or 
> write me email directly if they have any questions. I'd be very 
> glad to help them.

Hello Andrei, Ali,

Well, CS2 in D is over, and grades are in. Being a summer course 
it was conducted at twice the speed as in a regular semester.

Being the U of M there's enormous variation in background, 
current experience and ability, potential, etcetera etcetera, 
among students in the course. In the end registration had 
stabilized at 55 before the course started and (unusually) all of 
them finished it. There were a number of exceptional students of 
little experience in the class. There were also a number of 
students in the class with C++ experience that was more than 
beginner level. A majority of the students had come from the CS1 
course here which is Scheme based, and so they had experience 
mainly with functions, recursion and singly-linked lists.

My main observation is that there was a significantly greater 
level of inspiration engendered by using D as opposed to the 
usual alternatives. I and my TA saw a lot of the students in the 
lab and in office hours, and I made an effort to find out their 
reactions to using D, and they were very positive, especially so 
among those in about the top 2/3 or so of the class.

In our abstract data type implementations we made good use of D's 
superb dynamic arrays, and associative arrays, and we used both 
classes and structs; we made prolific use of operator overloading 
including signature constraints, and in an extra credit exercise 
we even had them write a simple opApply. We used classes to 
implement linked structures except at the end of the course. When 
I say "we" I mean that while I discussed topics on all scales and 
from abstract to concrete in lecture, the TA and I had them 
actively learn everything done via a long sequence of problems to 
solve in D, and some things were left to the lab.

At the end of the course I introduced pointers (to structs or to 
C-style arrays), and I discussed the connection between D and C. 
I also explained in detail how they could cripple their use of D 
and with small changes find themselves writing Java, and I gave 
an introductory discussion of the relationship of D to C++. In 
doing this I was pointing at their future courses: Java is the 
default language for a course here; in the machine architecture 
course they will use C; in the "Program Development" course they 
will use C++.

Language related issues that caught a significant minority of 
students out when solving the course's problems, despite 
explanation in lecture and lab, include the following. First up, 
no default constructor for structs, and what to do about it. This 
was complicated by the fact that in the Windows implementation of 
DMD it was possible to assign e.g. a new array directly to a 
struct variable, apparently contradicting the dictum of a fixed 
.init for structs. This lead to some writing code that needed 
non-trivial changes to run on the lab's Ubuntu machines. Second, 
the complexities of opCmp for classes, where a cast from Object 
is needed. We'd covered inheritance, but the need for this cast 
struck some as an unexpected deficiency in D, and we had to 
explain this many times to individual students struggling to make 
their code compile.

Overall, a significant number of students made this class a 
game-changing one for themselves, and were inspired and 
stimulated to learn more about algorithms and data structures, 
and to learn more about D. For example, we had them implement 
associative arrays as linked lists of pairs, then as hash tables 
using the previous implementation to do the work, and quite 
separately as a binary search trees. They had already implemented 
binary search trees with a single type parameter, and now having 
that type be a struct parameterized by a pair of types they could 
use the earlier solution to do the work. The result was a lot of 
very natural data abstraction, and, most exciting, types that 
looked built-in. This was very gratifying to many students. And, 
I should mention that the presence of operator overloading via 
opIndexAssign kept the associative array solutions simple enough 
for all students at this level, unlike what C++ would necessitate.

Ali Çehreli's tutorial played a central role supporting students 
especially during the first half of the course --- without it the 
course simply would not have worked, so "many thanks Ali" --- and 
an important part of that is its linearity --- it can be read 
with only backward dependencies. This meant that with hard work 
even students of little experience and only moderate current 
abilities could get up to speed, and we saw just that. It is hard 
to overstate this factor.

TDPL got some use during the second half of the course: most 
students acquired it and my impression is they did so because 
they had become inspired by D and wanted to use it to exert 
maximum leverage on the homework problems. All-in-all I saw a 
significant majority of the class inspired and excited in some 
cases by D itself because of its possibilities and 
expressiveness. This was told to me in office hours directly and 
repeatedly. I haven't had this experience with other languages 
used in the department.

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