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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