```{index} single: flowing (PDL) ``` ```{index} single: PDL::flowing ``` # flowing Turn on dataflow, so ndarrays derived from this one track its changes. my $b = $a->flowing->slice('0:4'); $a->set(2, 99); print $b->at(2); # 99 - $b followed the change Returns the ndarray, so it chains. Without `flowing`, a derived ndarray keeps whatever values it had when it was made. Views built by slicing and other index arithmetic follow their parent. Results of computed expressions such as `$a + $a` do not yet: the expression is evaluated once and the link is not retained, so a later write to `$a` will not refresh them.