Standard API for push_widen! pattern

There is a common pattern for handling not knowing the type of something produced in an iterative fashion, and gathering it up into the smallest container.
Basically you start with the container able something (This bit I think sometimes varies, it could be the first elements eltype, could be result of `@default_eltype`),
then you get the next thing you want to put in, if it fits then you push it in and continue,
if not then you make a new collection that can hold the union, copy everything over and then repeat.

The core of it is  in `push_widen!` but bits of the setup are in the `Set` construct, in `unique!` and in other places
https://github.com/JuliaLang/julia/blob/2d5741174ce3e6a394010d2e470e4269ca54607f/base/array.jl#L681-L716


We should look into a standard and public way to do this.
Its wanted in https://github.com/JuliaCollections/DataStructures.jl/pull/568#issuecomment-576384343

	function grow_to!(dest, itr)
	y = iterate(itr)
	y === nothing && return dest
	dest2 = empty(dest, typeof(y[1]))
	push!(dest2, y[1])
	grow_to!(dest2, itr, y[2])
	end

	function push_widen(dest, el)
	@_inline_meta
	new = sizehint!(empty(dest, promote_typejoin(eltype(dest), typeof(el))), length(dest))
	if new isa AbstractSet
	# TODO: merge back these two branches when copy! is re-enabled for sets/vectors
	union!(new, dest)
	else
	append!(new, dest)
	end
	push!(new, el)
	return new
	end

	function grow_to!(dest, itr, st)
	T = eltype(dest)
	y = iterate(itr, st)
	while y !== nothing
	el, st = y
	if el isa T \|\| typeof(el) === T
	push!(dest, el::T)
	else
	new = push_widen(dest, el)
	return grow_to!(new, itr, st)
	end
	y = iterate(itr, st)
	end
	return dest
	end

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Standard API for push_widen! pattern #34478

oxinabox
openedon Jan 22, 2020

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Standard API for push_widen! pattern #34478

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oxinaboxopenedon Jan 22, 2020

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