June 05, 2012
On Jun 4, 2012 8:43 PM, "Xinok" <xinok@live.com> wrote:
>
> I wonder in that case, is it even worth including in the language? For me
anyways, the whole point of these operators is to use them in expressions. Otherwise, why not simply write (i+=1)?

For pointers they are useful because they go up in units not bytes (although addition often does too).


June 05, 2012
On 06/04/2012 08:36 PM, Xinok wrote:
> The increment and decrement operators are highly dependent on operator
> precedence and associativity. If the actions are performed in a
> different order than the developer presumed, it could cause unexpected
> behavior.
>
> I had a simple idea to change the behavior of this operator. It works
> for the postfix operators but not prefix. Take the following code:
>
> size_t i = 5;
> writeln(i--, i--, i--);
>
> As of now, this writes "543". With my idea, instead it would write,
> "555". Under the hood, the compiler would rewrite the code as:
>
> size_t i = 5;
> writeln(i, i, i);
> --i;
> --i;
> --i;
>
> It decrements the variable after the current statement. While not the
> norm, this behavior is at least predictable. For non-static variables,
> such as array elements, the compiler could store a temporary reference
> to the variable so it can decrement it afterwards.
>
> I'm not actually proposing we actually make this change. I simply
> thought it was a nifty idea worth sharing.

The behaviour the language requires is that the function call executes as if the parameters were evaluated from left to right. This is exactly the behaviour you observe. What is the problem you want to fix?
June 05, 2012
2012/6/5 Jonathan M Davis <jmdavisProg@gmx.com>
>
>
> I think that Bernard is being a bit harsh, but in essence, I agree. Since
> the
> evaluation order of arguments is undefined, programmers should be aware of
> that
> and code accordingly. If they don't bother to learn, then they're going to
> get
> bitten, and that's life.
>
> Now, Walter _has_ expressed interest in changing it so that the order of
> evaluation for function arguments is fully defined as being left-to-right,
> which solves the issue. I'd still council against getting into the habit of
> writing code which relies on the order of evaluation for the arguments to a
> function, since it's so common for other languages not to define it (so
> that
> the compiler can better optimize the calls), and so getting into the habit
> of
> writing code which _does_ depend on the order of evalution for function
> arguments will cause you to write bad code you when you work in most other
> programming languages.
>
> As for treating pre or post-increment operators specially in some manner,
> that
> doesn't make sense. The problem is far more general than that. If we're
> going
> to change anything, it would be to make it so that the language itself
> defines
> the order of evaluation of function arguments as being left-to-right.
>
> - Jonathan M Davis
>

Agree completely!


June 06, 2012
On Tue, 05 Jun 2012 10:23:18 +0200, Mikael Lindsten wrote:

> 2012/6/5 Jonathan M Davis <jmdavisProg@gmx.com>
>>
>>
>> I think that Bernard is being a bit harsh, but in essence, I agree.
>> Since the
>> evaluation order of arguments is undefined, programmers should be aware
>> of that
>> and code accordingly. If they don't bother to learn, then they're going
>> to get
>> bitten, and that's life.
>>
>> Now, Walter _has_ expressed interest in changing it so that the order
>> of evaluation for function arguments is fully defined as being
>> left-to-right, which solves the issue. I'd still council against
>> getting into the habit of writing code which relies on the order of
>> evaluation for the arguments to a function, since it's so common for
>> other languages not to define it (so that
>> the compiler can better optimize the calls), and so getting into the
>> habit of
>> writing code which _does_ depend on the order of evalution for function
>> arguments will cause you to write bad code you when you work in most
>> other programming languages.
>>
>> As for treating pre or post-increment operators specially in some
>> manner, that
>> doesn't make sense. The problem is far more general than that. If we're
>> going
>> to change anything, it would be to make it so that the language itself
>> defines
>> the order of evaluation of function arguments as being left-to-right.
>>
>> - Jonathan M Davis
>>
>>
> Agree completely!
> <div class="gmail_quote">2012/6/5 Jonathan M Davis <span
> dir="ltr">&lt;<a href="mailto:jmdavisProg@gmx.com"
> target="_blank">jmdavisProg@gmx.com</a>&gt;</span><blockquote
> class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc
> solid;padding-left:1ex"> <div class="HOEnZb"><div class="h5">
> <br>
> </div></div>I think that Bernard is being a bit harsh, but in essence, I
> agree. Since the<br> evaluation order of arguments is undefined,
> programmers should be aware of that<br> and code accordingly. If they
> don&#39;t bother to learn, then they&#39;re going to get<br> bitten, and
> that&#39;s life.<br>
> <br>
> Now, Walter _has_ expressed interest in changing it so that the order
> of<br> evaluation for function arguments is fully defined as being
> left-to-right,<br> which solves the issue. I&#39;d still council against
> getting into the habit of<br> writing code which relies on the order of
> evaluation for the arguments to a<br> function, since it&#39;s so common
> for other languages not to define it (so that<br> the compiler can
> better optimize the calls), and so getting into the habit of<br> writing
> code which _does_ depend on the order of evalution for function<br>
> arguments will cause you to write bad code you when you work in most
> other<br> programming languages.<br>
> <br>
> As for treating pre or post-increment operators specially in some
> manner, that<br> doesn&#39;t make sense. The problem is far more general
> than that. If we&#39;re going<br> to change anything, it would be to
> make it so that the language itself defines<br> the order of evaluation
> of function arguments as being left-to-right.<br> <span
> class="HOEnZb"><font color="#888888"><br> - Jonathan M Davis<br>
> </font></span></blockquote></div><br><div>Agree
> completely!</div><div><br></div>


Ah noes, my eyes... HTML code... :-(


-- 
Dejan Lekic
  mailto:dejan.lekic(a)gmail.com
  http://dejan.lekic.org
June 06, 2012
On 4 June 2012 23:37, Jonathan M Davis <jmdavisProg@gmx.com> wrote:
> On Monday, June 04, 2012 23:22:26 Bernard Helyer wrote:
>> On Monday, 4 June 2012 at 20:44:42 UTC, bearophile wrote:
>> > Bernard Helyer:
>> >> If you find yourself using postfix increment/decrement operators in the same function call in multiple arguments, slap yourself firmly in the face and refactor that code.
>> >
>> > I think this is not acceptable, you can't rely on that, future
>> > D programers will not slap themselves and refactor their code.
>> > Some of the acceptable alternatives are:
>> > 1) Make post/pre increments return void. This avoid those
>> > troubles. I think Go language has chosen this. This is my
>> > preferred solution.
>> > 2) Turn that code into a syntax error for some other cause.
>> > 3) Design the language so post/pre increments give a defined
>> > effect on all D compilers on all CPUs. Walter since lot of time
>> > says this is planned for D. This leads to deterministic
>> > programs, but sometimes they are hard to understand and hard to
>> > translate (port) to other languages any way. Translating code
>> > to other languages is not irrelevant because D must be designed
>> > to make it easy to understand the semantics of the code.
>> >
>> > Bye,
>> > bearophile
>>
>> If people can't be bothered to understand what they write, they can go hang.
>
> I think that Bernard is being a bit harsh, but in essence, I agree. Since the evaluation order of arguments is undefined, programmers should be aware of that and code accordingly. If they don't bother to learn, then they're going to get bitten, and that's life.
>
> Now, Walter _has_ expressed interest in changing it so that the order of evaluation for function arguments is fully defined as being left-to-right, which solves the issue. I'd still council against getting into the habit of writing code which relies on the order of evaluation for the arguments to a function, since it's so common for other languages not to define it (so that the compiler can better optimize the calls), and so getting into the habit of writing code which _does_ depend on the order of evalution for function arguments will cause you to write bad code you when you work in most other programming languages.
>
> As for treating pre or post-increment operators specially in some manner, that doesn't make sense. The problem is far more general than that. If we're going to change anything, it would be to make it so that the language itself defines the order of evaluation of function arguments as being left-to-right.
>

"the language itself defines the order of evaluation of function arguments as being left-to-right" ... if the calling convention defines it.

For extern(D) the way you can expect order of evaluation to work in gdc generated code - for instance - is that each argument is evaluated from left to right, and if it has any side effects, then it is stored into a temporary prior to calling the function.

For extern(C) the order of evaluation is actually defined by the underlying architecture.  For example, i386 evaluates right-to-left, however other architectures (ie: ARM) perform left-to-right evaluation of function arguments.  Incidentally, I know there are a few tests in the testsuite that depend on the i386 behaviour, but that is something else to worry about.


Regards
-- 
Iain Buclaw

*(p < e ? p++ : p) = (c & 0x0f) + '0';
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