Is DMD 0.166 RC 1.0?

[Derek Parnell]

On Mon, 04 Sep 2006 15:44:52 -0700, Walter Bright wrote:

> Ivan Senji wrote:
>> Is there an example where replacing
>> 
>> f(a.prop);
>> 
>> with
>> 
>> auto x=a.prop; f(x); a.prop=x;
>> 
>> would be a bad thing to do, and could result in unexpected code, or hard 
>> to catch bugs.
>> Sure some aspects of this behavior should be well documented to avoid 
>> confusion (like the fact that the value is updated on function exit) but 
>> it is the same with most other feature.
>> 
>> To make myself clear: D can do without this feature but without it a 
>> simple:
>> 
>> write f(a.prop) -> compile&run happily
>> 
>> is replaced with
>> 
>> write f(a.prop) -> compile -> goto line with error -> figure out the 
>> error and how to fix it (might be hard the first time) ->
>> select "f(a.prop)" -> Ctrl-X -> write auto x=a.prop; f(x); a.prop=x; ->
>> compile&run (but less happily now)
> 
> I'd ask "why is f(x) returning a value in x?" That would normally be an 
> essential part of the behavior of the function, so:
> 	f(3)
> should return an error, shouldn't it? If modifying its argument is an 
> essential behavior of the function, and the argument is not modifiable, 
> probably the programmer made a mistake and the compiler should not paper 
> it over. And the same for every other argument that isn't an lvalue (and 
> so cannot be set).
> 
> If you find yourself writing:
> 
>     auto x=a.prop; f(x); a.prop=x;
> 
> I would seriously question what is going on with f(). It's a big flag 
> that something is wrong either with f() or with the usage of f(). I 
> would not want the compiler papering it over.

What a load of BS. The user of 'prop' does not need to know how it's been
implemented. 

class A
{
   int prop;
}

class B 
{
    private int q;
    void prop(int x) { q = x; }
    int prop() { return q; }
}

void f(inout int x)
{
    if (x < 0)
       x = -x;
}

A a = new A;
B b = new B;

f(a.prop);  // okay
f(b.prop);  // fubar




-- 
Derek Parnell
Melbourne, Australia
"Down with mediocrity!"