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.
