• "Tobias Pankrath" <tobias pankrath.net> Jun 02 2012
• "bearophile" <bearophileHUGS lycos.com> Jun 02 2012
• "Tobias Pankrath" <tobias pankrath.net> Jun 02 2012
• Artur Skawina <art.08.09 gmail.com> Jun 02 2012

"Tobias Pankrath" <tobias pankrath.net> writes:

consider this:


------------
import std.stdio;
import std.string;

alias void delegate() dlgt;

int main()
{
         dlgt[] dgs;
         string[] lines = ["line A", "line B", "line C"];
         foreach(line; lines)
         {
                 writeln(line);
                 dgs ~=  { writeln(line); };
         }

         foreach(dg; dgs) { dg(); }
         return 0;
}

-----------

It prints every line in line and stores a delegate that does the 
same.
The output is:

line A
line B
line C
line C
line C
line C

I want it to print every line twice. How can I store the string 
of the current iteration with a delegate? I tried dup'ing into a 
local, which didn't help.

Thank you for your advice.

"bearophile" <bearophileHUGS lycos.com> writes:

Tobias Pankrath:

 How can I store the string of the current iteration with a 
 delegate?


You need to create a closure (D main returns 0 automatically):


import std.stdio, std.string;

void main() {
     auto lines = ["line A", "line B", "line C"];
     void delegate()[] delegates;

     foreach (line; lines) {
         writeln(line);
         delegates ~= ((in string myLine) => { writeln(myLine); 
})(line);
     }

     foreach (deleg; delegates)
         deleg();
}


Bye,
bearophile

"Tobias Pankrath" <tobias pankrath.net> writes:

Thank you. That works.

Artur Skawina <art.08.09 gmail.com> writes:

On 06/02/12 14:01, Tobias Pankrath wrote:
 consider this:
 
 
 ------------
 import std.stdio;
 import std.string;
 
 alias void delegate() dlgt;
 
 int main()
 {
         dlgt[] dgs;
         string[] lines = ["line A", "line B", "line C"];
         foreach(line; lines)
         {
                 writeln(line);
                 dgs ~=  { writeln(line); };
         }
 
         foreach(dg; dgs) { dg(); }
         return 0;
 }
 
 -----------
 
 It prints every line in line and stores a delegate that does the same.
 The output is:
 
 line A
 line B
 line C
 line C
 line C
 line C
 
 I want it to print every line twice. How can I store the string of the current
iteration with a delegate? I tried dup'ing into a local, which didn't help.


   dgs ~= (string l) { return { writeln(l); }; }(line);

This isn't really much different from
http://d.puremagic.com/issues/show_bug.cgi?id=2043
but I'm not convinced the compiler should be cloning the variables here (ie if
that "bug"
really is a bug); it certainly can be surprising though.

artur