Minor fix: FlagFirst‘s state is always (false, ...)

[mschauer]

FlagFirst‘s state is always (false, ...)

[codecov-io]

Codecov Report

Merging #72 into master will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #72   +/-   ##
=======================================
  Coverage   72.95%   72.95%           
=======================================
  Files           1        1           
  Lines         281      281           
=======================================
  Hits          205      205           
  Misses         76       76           

Impacted Files	Coverage Δ
src/IterTools.jl	72.95% <100.00%> (ø)

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[mschauer]

Btw. I compared your implementation

function iterate(ff::FlagFirst, state = (true, ))
    isfirst, rest = first(state), tail(state)
    elt, nextstate = @ifsomething iterate(ff.iter, rest...)
    (isfirst, elt), (isfirst & false, nextstate)
end

with one I had myself, using two functions

function Base.iterate(ff::FlagFirst)
    elt, state = @ifsomething iterate(ff.iter)
    (true, elt), state
end
function Base.iterate(t::FlagFirst, state)
    elt, state = @ifsomething iterate(ff.iter, state)
    (false, elt), state
end

and while IterTools's implementation is more demanding on the optimiser (harder to proof that a branch "if isfirst" can be removed from the body of a loop over the iterator, both create same code. In short: all is well.

[iamed2]

IterTools's implementation is more demanding on the optimiser (harder to proof that a branch "if isfirst" can be removed from the body of a loop over the iterator

Yeah I think Tim Holy brought that up when I made my iterators blog. I haven't really come up with a good way to do it both compactly and without splatting, but I also haven't thought about it too hard.

[mschauer]

Let's change it actually into the two function form, that is easier to reason about (both for humans and compilers I guess)