• bearophile <bearophileHUGS lycos.com> Mar 24 2011
• spir <denis.spir gmail.com> Mar 24 2011
• Jesse Phillips <jessekphillips+D gmail.com> Mar 24 2011
• Jacob Carlborg <doob me.com> Mar 25 2011
• bearophile <bearophileHUGS lycos.com> Mar 25 2011
• Jacob Carlborg <doob me.com> Mar 25 2011
• Kagamin <spam here.lot> Mar 25 2011
• Kai Meyer <kai unixlords.com> Mar 28 2011
• bearophile <bearophileHUGS lycps.com> Mar 28 2011

bearophile <bearophileHUGS lycos.com> writes:

A little quiz for people here: guess the output of this little D2 program (it
compiles correctly and doesn't crash at run time, so it's a fair question):


import std.typecons: tuple;
import std.c.stdio: printf;

auto foo() {
    printf("foo\n");
    return tuple(1, 2);
}

void main() {
    foreach (x; foo().tupleof)
        printf("%d\n", x);
}


Bye,
bearophile

spir <denis.spir gmail.com> writes:

On 03/25/2011 01:50 AM, bearophile wrote:
 A little quiz for people here: guess the output of this little D2 program (it
compiles correctly and doesn't crash at run time, so it's a fair question):


 import std.typecons: tuple;
 import std.c.stdio: printf;

 auto foo() {
      printf("foo\n");
      return tuple(1, 2);
 }

 void main() {
      foreach (x; foo().tupleof)
          printf("%d\n", x);
 }


lol, would never haver guessed

Denis
-- 
_________________
vita es estrany
spir.wikidot.com

Jesse Phillips <jessekphillips+D gmail.com> writes:

bearophile Wrote:

 A little quiz for people here: guess the output of this little D2 program (it
compiles correctly and doesn't crash at run time, so it's a fair question):
 
 
 import std.typecons: tuple;
 import std.c.stdio: printf;
 
 auto foo() {
     printf("foo\n");
     return tuple(1, 2);
 }
 
 void main() {
     foreach (x; foo().tupleof)
         printf("%d\n", x);
 }


Starting from main. As we are performing a foreach over a tuple this will need
to happen at compilation. As their are many bugs with compile time foreach I
would think this code evaluates to nothing and thus the program prints nothing.

However if that is working then I would expect foo() to be executed at
compile-time which would mean 'foo' might be printed during compilation. As
tupleof is supposed to return a type tuple, I'm unsure what gibberish printing
it as a decimal would do.

The other likely possibility is that the foreach is unrolled into code like:

x = foo().tupleof[0]
print...
x = foo().tupleof[1]
print...

where .tupleof is some other fancy runtime thing. In this case you would get
foo\nnumber\nfoo\nnumber...

------

So yeah, from that code I have no idea what it is supposed to do. But I am not
surprised by its behavior.

Jacob Carlborg <doob me.com> writes:

On 2011-03-25 01:50, bearophile wrote:
 A little quiz for people here: guess the output of this little D2 program (it
compiles correctly and doesn't crash at run time, so it's a fair question):


 import std.typecons: tuple;
 import std.c.stdio: printf;

 auto foo() {
      printf("foo\n");
      return tuple(1, 2);
 }

 void main() {
      foreach (x; foo().tupleof)
          printf("%d\n", x);
 }


 Bye,
 bearophile


I would guess it prints the values of all the fields in the struct 
returned by "tuple".

-- 
/Jacob Carlborg

bearophile <bearophileHUGS lycos.com> writes:

Jacob Carlborg:

 I would guess it prints the values of all the fields in the struct 
 returned by "tuple".


That was of course my purpose, because tuples are a way to implement multiple
return values, and in some situations I want to print all the items of such
return tuple, on separated lines, for debugging purposes, etc. But
unfortunately (for me too) that's not the right answer. Try again... I have
found a little surprise.

Bye,
bearophile

Jacob Carlborg <doob me.com> writes:

On 2011-03-25 12:32, bearophile wrote:
 Jacob Carlborg:

 I would guess it prints the values of all the fields in the struct
 returned by "tuple".


 That was of course my purpose, because tuples are a way to implement multiple
return values, and in some situations I want to print all the items of such
return tuple, on separated lines, for debugging purposes, etc. But
unfortunately (for me too) that's not the right answer. Try again... I have
found a little surprise.

 Bye,
 bearophile


I'm not just meaning the expected values you pass in to the function, 
I'm also referring to any additional fields that might be present in the 
struct.

-- 
/Jacob Carlborg

Kagamin <spam here.lot> writes:

bearophile Wrote:

 A little quiz for people here: guess the output of this little D2 program (it
compiles correctly and doesn't crash at run time, so it's a fair question):
 
 
 import std.typecons: tuple;
 import std.c.stdio: printf;
 
 auto foo() {
     printf("foo\n");
     return tuple(1, 2);
 }
 
 void main() {
     foreach (x; foo().tupleof)
         printf("%d\n", x);
 }
 
 
 Bye,
 bearophile


According to docs tupleof returns type tuple, but TypeTuple doesn't seem to be
iteratable.

Kai Meyer <kai unixlords.com> writes:

On 03/24/2011 06:50 PM, bearophile wrote:
 A little quiz for people here: guess the output of this little D2 program (it
compiles correctly and doesn't crash at run time, so it's a fair question):


 import std.typecons: tuple;
 import std.c.stdio: printf;

 auto foo() {
      printf("foo\n");
      return tuple(1, 2);
 }

 void main() {
      foreach (x; foo().tupleof)
          printf("%d\n", x);
 }


 Bye,
 bearophile


That's pretty cool :) Seems like we should be able to expect the same 
behavior in all of these, but that doesn't appear to be the case at all.



import std.typecons: tuple;
import std.c.stdio: printf;

auto foo() {
     printf("foo\n");
     return tuple(1, 2);
}

void main() {
     printf("-----\n");
     foreach (x; foo().tupleof)
         printf("%d\n", x);
     printf("-----\n");
     auto f = foo();
     printf("-----\n");
     foreach (x; f.tupleof)
         printf("%d\n", x);
     printf("-----\n");
     auto f2 = foo().tupleof;
     printf("-----\n");
     foreach (x; f2)
         printf("%d\n", x);
     printf("-----\n");
}

bearophile <bearophileHUGS lycps.com> writes:

Kai Meyer:

      auto f2 = foo().tupleof;


Thank you. From the output of this line of code the problem seems not caused by
the static foreach.

Bye,
bearophile