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digitalmars.D.learn - foreach, tupleof

reply Ellery Newcomer <ellery-newcomer utulsa.edu> writes:
Hello.

In D1, this code fails:

void foo(S)(ref S s){
   foreach(ref k; s.tupleof){
     k = 1;
   }
}

struct K{
   int g;
}

void main(){
   K k;
   foo(k);
   assert(k.g == 1);
}


test.d(5): Error: no storage class for value k

(referring to 'k = 1;')

Is this an expected error, and is there a good way to get the semantics 
to actually work?
Mar 07 2010
parent reply Jacob Carlborg <doob me.com> writes:
On 3/7/10 19:11, Ellery Newcomer wrote:

 Hello.

 In D1, this code fails:

 void foo(S)(ref S s){
 foreach(ref k; s.tupleof){
 k = 1;
 }
 }

 struct K{
 int g;
 }

 void main(){
 K k;
 foo(k);
 assert(k.g == 1);
 }


 test.d(5): Error: no storage class for value k

 (referring to 'k = 1;')

 Is this an expected error, and is there a good way to get the semantics
 to actually work?


It's a bug: http://d.puremagic.com/issues/show_bug.cgi?id=2411
You can use the following code as a workaround:

foreach (i, dummy ; s.tupleof)
	s.tupleof[i] = 1;
Mar 07 2010
parent reply Ellery Newcomer <ellery-newcomer utulsa.edu> writes:
On 03/07/2010 12:23 PM, Jacob Carlborg wrote:

 On 3/7/10 19:11, Ellery Newcomer wrote:

 Hello.

 In D1, this code fails:

 void foo(S)(ref S s){
 foreach(ref k; s.tupleof){
 k = 1;
 }
 }

 struct K{
 int g;
 }

 void main(){
 K k;
 foo(k);
 assert(k.g == 1);
 }


 test.d(5): Error: no storage class for value k

 (referring to 'k = 1;')

 Is this an expected error, and is there a good way to get the semantics
 to actually work?


 It's a bug: http://d.puremagic.com/issues/show_bug.cgi?id=2411
 You can use the following code as a workaround:

 foreach (i, dummy ; s.tupleof)
 s.tupleof[i] = 1;


Totally awesome! Thanks a float.infinity!
Mar 07 2010
parent reply Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Sun, Mar 7, 2010 at 19:53, Ellery Newcomer <ellery-newcomer utulsa.edu>wrote:


 On 03/07/2010 12:23 PM, Jacob Carlborg wrote:


 It's a bug: http://d.puremagic.com/issues/show_bug.cgi?id=2411
 You can use the following code as a workaround:

 foreach (i, dummy ; s.tupleof)
 s.tupleof[i] = 1;


 Totally awesome! Thanks a float.infinity!


I remember spending *weeks* (well, OK, *hours*) trying to find a way to do
such a mapping after trying the first foreach, and getting some recursive
template to work... Only to find this static foreach trick, looking at
Phobos code (for D2) some month after. It sent ripples in all my code...

As a side note, it works for any tuple: those created by .tupleof, but also
the variadic template parameters, the expansion of a std.typecons.Tuple
(D2), those created by templates, etc. So you can do:

void reinitialize(T...)(ref T ts) // Variadic template
{
    foreach(i, Type; T) ts[i] = T[i].init; // iterating on the components of
T.
}

int a = 1;
char c = 'a';
string s = "abc";

reinitialize(a,c,s);

assert(a = 0); // int.init
assert(c =  char.init); // is there a literal for char.init? '' doesn't
work.
assert(s="");


Philippe
Mar 08 2010
parent reply bearophile <bearophileHUGS lycos.com> writes:
Philippe Sigaud:

 assert(c =  ); // is there a literal for char.init? '' doesn't
 work.


I think it's '\xFF' but I don't know if it may change in future, so using
char.init is probably better, more readable, more explicit in its purpose, and
less prone to typing bugs.

Bye,
bearophile
Mar 08 2010
parent Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Mon, Mar 8, 2010 at 22:11, bearophile <bearophileHUGS lycos.com> wrote:


 Philippe Sigaud:

 assert(c =  ); // is there a literal for char.init? '' doesn't
 work.


 I think it's '\xFF' but I don't know if it may change in future, so using
 char.init is probably better, more readable, more explicit in its purpose,
 and less prone to typing bugs.

 Thanks. It's an invalid char, as NaN for floats?
Mar 08 2010