On Thursday, 12 May 2016 at 10:17:19 UTC, xtreak wrote:
Thanks a lot. Can you kindly elaborate a little more on
File.byLine with an example of the scenario so that I don't get
bitten by it. File.byLine.array works as expected for me. A
little more explanation on the permutations will also be
helpful since joiner.map!array converts the subranges to
arrays, so does joiner work by mutating state if so how does it
do.
With some ranges the value they return by .front is only valid
until the next call to popFront(). For example, File.byLine()
reuses its buffer so after popFront() is called the buffer
contains different data and if you had references to the contents
of previously returned value they become invalid. This is why
byLineCopy() was added. In the same vein permutations() returns a
range that has a mutable array of indices inside, which changes
every time popFront() is called, and since every value returned
by its .front refers to that indices array, if you collect such
permutations they will all use the same array of indices and show
the same order of elements, the same permutation.
Because of this mutable nature of some ranges it's important to
understand in which order calls to .front and .popFront() happen.
The array() function calls popFront on its input in a loop,
consuming the mutable ranges, while map() does not. So in
r.map!f.array
function f will receive different valid values, before they get
invalidated in the loop of array(). But if they contain
references to something mutable, it makes sense to make copies
before the thing they refer to mutates.
