BreakAt iterator definition

breakat.jl

import Base.Iterators: start, next, done, eltype, iteratoreltype, iteratorsize, SizeUnknown

struct BreakAt{P,I}
    pred::P
    itr::I
end

breakat(pred, itr) = BreakAt(pred, itr)

@inline start(b::BreakAt) = start_breakat(b.pred, b.itr)
@inline function start_breakat(pred, itr)
    s = start(itr)
    if !done(itr, s)
        v, t = next(itr, s)
        return pred(v) ? (true, v, t) : (false, v, t)
    end
    return (true, v, t)
end

@inline next(b::BreakAt, s) = advance_breakat(b.pred, b.itr, s)
@inline function advance_breakat(pred, itr, st)
    _, v, s = st
    if !done(itr, s)
        w, t = next(itr, s)
        return pred(w) ? (v, (true, w, t)) : (v, (false, w, t))
    end
    return (true, v, s)
end

@inline done(b::BreakAt, s) = s[1]

eltype(::Type{BreakAt{F,I}}) where {F, I} = eltype(I)
iteratoreltype(::Type{BreakAt{F,I}}) where {F, I} = iteratoreltype(I)
iteratorsize(::Type{<:BreakAt}) = SizeUnknown()