Which D features to emphasize for academic review article

[Mehrdad]

On Saturday, 11 August 2012 at 05:41:23 UTC, Walter Bright wrote:
> On 8/10/2012 9:55 PM, F i L wrote:
>> On the first condition, without an 'else z = ...', or if the 
>> condition was removed at a later time, then you'll get a 
>> compiler error and be forced to explicitly assign 'z' 
>> somewhere above using it. So C# and D work in "similar" ways 
>> in this respect except that C# catches these issues at 
>> compile-time, whereas in D you need to:
>>   1. run the program
>>   2. get bad result
>>   3. hunt down bug
>
> However, and I've seen this happen, people will satisfy the 
> compiler complaint by initializing the variable to any old 
> value (usually 0), because that value will never get used. 
> Later, after other things change in the code, that value 
> suddenly gets used, even though it may be an incorrect value 
> for the use.


Note to Walter:

You're obviously correct that you can make an arbitrarily complex 
program to make it too difficult for the compiler to enforce 
initialization, the way C# does (and gives up in some cases).

What you seem to be missing is that the issue you're saying is 
correct in theory, but too much of a corner case in practice.

C#/Java programmers ___rarely___ run into the sort of issue 
you're mentioning, and even when they do, they don't have nearly 
as much of a problem with fixing it as you seem to think.

The only reason you run into this sort of problem (assuming you 
do, and it's not just a theoretical discussion) is that you're in 
the C/C++ mindset, and using variables in the C/C++ fashion.
If you were a "C#/Java Programmer" instead of a "C++ Programmer", 
you simply _wouldn't_ try to make things so complicated when 
coding, and you simply _wouldn't_ run into these problems the way 
you /think/ you would, as a C++ programmer.


Regardless, it looks to me like you two are arguing for two 
orthogonal issues:

F i L:  The compiler should detect uninitialized variables.
Walter: The compiler should choose initialize variables with NaN.


What I'm failing to understand is, why can't we have both?

1. Compiler _warns_ about "uninitialized variables" (or scalars, 
at least) the same way C# and Java do, __unless__ the user takes 
the address of the variable, in which case the compiler gives up 
trying to detect the flow (like C#).
Bonus points: Try to detect a couple of common cases (e.g. 
if/else) instead of giving up so easily.

2. In any case, the compiler initializes the variable with 
whatever default value Walter deems useful.


Then you get the best of both worlds:

1. You force the programmer to manually initialize the variable 
in most cases, forcing him to think about the default value. It's 
almost no trouble for

2. In the cases where it's not possible, the language helps the 
programmer catch bugs.


Why the heck D avoids #1, I have no idea.

It's one of the _major_ features of C# and Java that help promote 
correctness, and #1 looks orthogonal to #2 to me.



For users who don't like #1: They can suppress the warning. 
Nothing lost, anyway.
For users who DO like #1: They can turn it into an error. A lot 
to be gained.