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WIP: Preserve concrete Union types in collect() with generators #23940

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WIP: Preserve concrete Union types in collect() with generators #23940

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16 changes: 14 additions & 2 deletions base/array.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -664,6 +664,14 @@ end
_array_for(::Type{T}, itr, ::HasLength) where {T} = Array{T,1}(Int(length(itr)::Integer))
_array_for(::Type{T}, itr, ::HasShape) where {T} = similar(Array{T}, indices(itr))

function _isconcreteunion(::Type{T}) where T
if T isa Union
_isconcreteunion(T.a) && _isconcreteunion(T.b)
else
isconcrete(T)
end
end

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We already have Base.isbitsunion for this.

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This one is slightly different, it also includes things like Union{String, Void}.

function collect(itr::Generator)
isz = iteratorsize(itr.iter)
et = _default_eltype(typeof(itr))
Expand All @@ -675,7 +683,9 @@ function collect(itr::Generator)
return _array_for(et, itr.iter, isz)
end
v1, st = next(itr, st)
collect_to_with_first!(_array_for(typeof(v1), itr.iter, isz), v1, itr, st)
S = _default_eltype(typeof(itr))
T = _isconcreteunion(S) ? S : typeof(v1)
collect_to_with_first!(_array_for(T, itr.iter, isz), v1, itr, st)
end
end

Expand All @@ -688,7 +698,9 @@ function _collect(c, itr, ::EltypeUnknown, isz::Union{HasLength,HasShape})
return _similar_for(c, _default_eltype(typeof(itr)), itr, isz)
end
v1, st = next(itr, st)
collect_to_with_first!(_similar_for(c, typeof(v1), itr, isz), v1, itr, st)
S = _default_eltype(typeof(itr))
T = _isconcreteunion(S) ? S : typeof(v1)
collect_to_with_first!(_similar_for(c, T, itr, isz), v1, itr, st)
end

function collect_to_with_first!(dest::AbstractArray, v1, itr, st)
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4 changes: 4 additions & 0 deletions test/arrayops.jl
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Expand Up @@ -1207,6 +1207,10 @@ end
@test isequal([1,2,3], [a for (a,b) in enumerate(2:4)])
@test isequal([2,3,4], [b for (a,b) in enumerate(2:4)])

@test [s for s in Union{String, Void}["a", nothing]] isa Vector{Union{String, Void}}
@test [s for s in Union{String, Void}["a"]] isa Vector{Union{String, Void}}
@test [s for s in Vector{Union{String, Void}}()] isa Vector{Union{String, Void}}

@testset "comprehension in let-bound function" begin
let x⊙y = sum([x[i]*y[i] for i=1:length(x)])
@test [1,2] ⊙ [3,4] == 11
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42 changes: 42 additions & 0 deletions test/functional.jl
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Expand Up @@ -142,3 +142,45 @@ end
for n = 0:5:100-q-d
for p = 100-q-d-n
if p < n < d < q] == [(50,30,15,5), (50,30,20,0), (50,40,10,0), (75,20,5,0)]

@testset "return type of map() and collect() on generators" begin
x = ["a", "b"]
res = @inferred collect(s for s in x)
@test res isa Vector{String}
res = @inferred map(identity, x)
@test res isa Vector{String}
res = @inferred collect(s === nothing for s in x)
@test res isa Vector{Bool}
res = @inferred map(s -> s === nothing, x)
@test res isa Vector{Bool}

y = Union{String, Void}["a", nothing]
f(::Void) = nothing
f(s::String) = s == "a"
res = @inferred collect(s for s in y)
@test res isa Vector{Union{String, Void}}
res = @inferred map(identity, y)
@test res isa Vector{Union{String, Void}}
res = @inferred collect(s === nothing for s in y)
@test res isa Vector{Bool}
res = @inferred map(s -> s === nothing, y)
@test res isa Vector{Bool}
res = @inferred collect(f(s) for s in y)
@test res isa Vector{Union{Bool, Void}}
res = @inferred map(f, y)
@test res isa Vector{Union{Bool, Void}}

y[2] = "c"
res = @inferred collect(s for s in y)
@test res isa Vector{Union{String, Void}}
res = @inferred map(identity, y)
@test res isa Vector{Union{String, Void}}
res = @inferred collect(s === nothing for s in y)
@test res isa Vector{Bool}
res = @inferred map(s -> s === nothing, y)
@test res isa Vector{Bool}
res = @inferred collect(f(s) for s in y)
@test res isa Vector{Union{Bool, Void}}
res = @inferred map(f, y)
@test res isa Vector{Union{Bool, Void}}
end