• Jason den Dulk (22/22) Aug 27 2013 Hi
• monarch_dodra (48/71) Aug 27 2013 No. It is incorrect behavior. It is a *very* big problem we know
• Jesse Phillips (3/10) Aug 28 2013 What monarch said, though std.range.refRange() may be of interest:
• H. S. Teoh (7/21) Aug 28 2013 That currently doesn't work too well if you use any RNG members other

"Jason den Dulk" <public2 jasondendulk.com> writes:

Hi

This code

   foreach (j; 0..5)
     writeln(rndGen().take(5));
   writeln(uniform(0, 1024));
   foreach (j; 0..5)
     writeln(rndGen().take(5));

produces this output

   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   813
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]

Is this correct behaviour? It appears a little inconsistant to me.

Regards
Jason

"monarch_dodra" <monarchdodra gmail.com> writes:

On Tuesday, 27 August 2013 at 12:59:19 UTC, Jason den Dulk wrote:
 Hi

 This code

   foreach (j; 0..5)
     writeln(rndGen().take(5));
   writeln(uniform(0, 1024));
   foreach (j; 0..5)
     writeln(rndGen().take(5));

 produces this output

   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   [3410716173, 2484862302, 280352965, 1820347603, 850366086]
   813
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]
   [2484862302, 280352965, 1820347603, 850366086, 604192828]

 Is this correct behaviour? It appears a little inconsistant to 
 me.

 Regards
 Jason

No. It is incorrect behavior. It is a *very*  big problem we know 
about, and are trying to fix. The problem (arguably) is so big, 
it warrants making a brand new random2 module.

Long story short: The current PRNG's a value types. This means 
that when you pass them around (by value) you are duplicating 
them. The fix (for us) is to make them all  reference types, so 
that passign them around doesn't duplicate them.

In the meantime, workarounds include: Generating a new PRGN every 
time you need a new sequence, or creating your own wrapper around 
rndGen();

struct GoodPrng
{
     enum empty = false;
     void popFront()
     {
         rndGen().popFront();
     }
     auto front()  property
     {
         return rndGen().front;
     }
}
GoodPrng goodPrng()
{
     return GoodPrng();
}

This should work:
void main()
{
     foreach (j; 0..5)
         writeln(GoodPrng().take(5));
     writeln(uniform(0, 1024));
     foreach (j; 0..5)
         writeln(GoodPrng().take(5));
}

[47855835, 916983782, 2006604655, 2074198403, 772414269]
[2220086136, 3393309461, 3644080841, 1053550911, 2595436893]
[3782843356, 2688374946, 3181159978, 628742771, 1672837671]
[192566424, 3205182805, 521392827, 1528745543, 2713259487]
[1188847012, 820882915, 1616362385, 837154982, 553045938]
400
[2350166972, 951558946, 1940218749, 1245693761, 3154088887]
[4184834298, 2262977512, 3554532516, 3345988025, 1171565042]
[3698692802, 538668063, 4044473111, 666762521, 865383943]
[3357865623, 3653338316, 276404459, 1764534280, 1999822962]
[1118055308, 3030179246, 3422085781, 4056620356, 201644357]

We apologize for the inconvenience.

"Jesse Phillips" <Jesse.K.Phillips+D gmail.com> writes:

On Tuesday, 27 August 2013 at 12:59:19 UTC, Jason den Dulk wrote:
 Hi

 This code

   foreach (j; 0..5)
     writeln(rndGen().take(5));
   writeln(uniform(0, 1024));
   foreach (j; 0..5)
     writeln(rndGen().take(5));

What monarch said, though std.range.refRange() may be of interest:

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Wed, Aug 28, 2013 at 06:18:01PM +0200, Jesse Phillips wrote:
 On Tuesday, 27 August 2013 at 12:59:19 UTC, Jason den Dulk wrote:
Hi

This code

  foreach (j; 0..5)
    writeln(rndGen().take(5));
  writeln(uniform(0, 1024));
  foreach (j; 0..5)
    writeln(rndGen().take(5));

 
 What monarch said, though std.range.refRange() may be of interest:
 


That currently doesn't work too well if you use any RNG members other
than the standard range API, due to:

	http://d.puremagic.com/issues/show_bug.cgi?id=10888


T

-- 
Ignorance is bliss... until you suffer the consequences!