HasLength trait for some Flatten iterators by mschauer · Pull Request #22691 · JuliaLang/julia

mschauer · 2017-07-06T11:49:31Z

It is worthwhile to give some Flatten-ed iterators the trait HasLength, if the elements of the iterator which gets flattened are iteratables with type-static length, for example Tuples. This PR does this for iterators with elements of type Tuple and Number.

This functionality can then be extended by packages defining iterators with type-encoded length.
For example it allows https://github.com/JuliaArrays/StaticArrays.jl to flatten a Vector of SVector's efficiently.
Replaces #16680

nalimilan · 2017-07-06T11:59:55Z

base/iterators.jl

 _flatteneltype(I, ::HasEltype) = iteratoreltype(eltype(I))
 _flatteneltype(I, et) = EltypeUnknown()

+flatten_iteratorsize(::Union{HasShape, HasLength}, b::Type{T}) where {T<:Tuple} = HasLength()


Split lines at 92 characters. Here, you can do ::Type{<:Tuple} to save some space.

Sacha0 · 2017-07-06T20:25:00Z

base/iterators.jl

+flatten_iteratorsize(::Union{HasShape, HasLength}, b::Type{T}) where {T<:Tuple} = HasLength()
+flatten_iteratorsize(::Union{HasShape, HasLength}, b::Type{T}) where {T<:Number} = HasLength()
+flatten_iteratorsize(a, b) = SizeUnknown()
+flatten_length(f, ::Type{T}) where {T<:Tuple} = isleaftype(T) ? nfields(T)*length(f.it) : throw(ArgumentError("Cannot compute length of a tuple-type which is not a leaf-type"))


Line length here as well. Perhaps write this method definition long-form with an if-else?

Sacha0 · 2017-07-06T20:25:34Z

base/iterators.jl

+flatten_length(f, ::Type{T}) where {T<:Tuple} = isleaftype(T) ? nfields(T)*length(f.it) : throw(ArgumentError("Cannot compute length of a tuple-type which is not a leaf-type"))
+flatten_length(f, ::Type{T}) where {T<:Number} = length(f.it)
+length(f::Flatten{I}) where {I} = flatten_length(f, eltype(I))
+iteratorsize(::Type{Flatten{I}}) where {I} = isleaftype(eltype(I)) ? flatten_iteratorsize(iteratorsize(I), eltype(I)) : SizeUnknown() # eltype is always defined


Likewise here re. line length. Perhaps also better as a long-form method definition with an if-else? :)

Sacha0 · 2017-07-06T20:26:04Z

test/iterators.jl

 @test collect(flatten(Any[flatten(Any[1:2, 6:5]), flatten(Any[6:7, 8:9])])) == Any[1,2,6,7,8,9]
 @test collect(flatten(Any[2:1])) == Any[]
 @test eltype(flatten(UnitRange{Int8}[1:2, 3:4])) == Int8
+@test length(flatten(zip(1:3,4:6))) == 6


A space between the arguments to zip would aid visual parsing :).

Sacha0 · 2017-07-06T20:26:59Z

test/iterators.jl

 @test eltype(flatten(UnitRange{Int8}[1:2, 3:4])) == Int8
+@test length(flatten(zip(1:3,4:6))) == 6
 @test_throws ArgumentError collect(flatten(Any[]))
+@test_throws ArgumentError length(flatten(NTuple[(1,),()])) # #16680


Likewise here, a space following the comma between Tuples might make this easier to parse visually? :)

For future reference: https://en.wikipedia.org/wiki/Klempen

rfourquet · 2017-07-07T09:30:25Z

base/iterators.jl

-flatten_length(f, ::Type{T}) where {T<:Tuple} = isleaftype(T) ? nfields(T)*length(f.it) : throw(ArgumentError("Cannot compute length of a tuple-type which is not a leaf-type"))
+
+function flatten_length(f, ::Type{<:Tuple})
+    if !isleaftype(T)


T is not defined anymore, adding T::Type{<:Tuple} in the signature should work

Isn't function flatten_length(f, ::Type{T}) where T<:Tuple better?

Sorry, I did not pay attention here

No problem!

@fredrikekre you mean better in style, or... in efficiency?

ok, I thought T::Type may be less efficient than ::Type{T} where T, but that it was not the case for T::Type{<:Tuple} which should be specialized for each different type...

rfourquet · 2017-07-07T09:36:01Z

base/iterators.jl

+    end
+    nfields(T)*length(f.it)
+end
+flatten_length(f, ::Type{T}) where {T<:Number} = length(f.it)


flatten_length(f, ::Type{<:Number}) = length(f.it) ? (just a suggestion!)

rfourquet · 2017-07-07T09:42:06Z

base/iterators.jl

+    nfields(T)*length(f.it)
+end
+flatten_length(f, ::Type{T}) where {T<:Number} = length(f.it)
+length(f::Flatten{I}) where {I} = flatten_length(f, eltype(I))


For non-(number, tuple), this will throw a MethodError right? why not a fall-ball flatten_length which throws a more informative message?

rfourquet · 2017-07-12T08:41:05Z

test/iterators.jl

+@test length(flatten(zip(1:3, 4:6))) == 6
 @test_throws ArgumentError collect(flatten(Any[]))
+@test_throws ArgumentError length(flatten(NTuple[(1,), ()])) # #16680
+@test_throws ArgumentError length(flatten([[1],[1]]))


rfourquet · 2017-07-12T08:52:24Z

base/iterators.jl

+end
+flatten_length(f, ::Type{<:Number}) = length(f.it)
+flatten_length(f, T) = throw(ArgumentError(
+            "Iterates of the argument to Flatten are not known to have constant length"))


Strange indentation, I think this would be better with only 4 spaces

"Iteratees" wouldn't be the correct word here?

and as you have a T, you might as well report it in the message, e.g. "Iteratees (of type $T) ...

Flatten is private no? could be better to use flatten.

Iteratees would sound funny, even if possibly correct

rfourquet · 2017-07-12T08:55:29Z

base/iterators.jl

+flatten_iteratorsize(a, b) = SizeUnknown()
+
+function flatten_length(f, ::Type{T}) where {T<:Tuple}
+    if !isleaftype(T)


Do you know if this check is statically resolved?

From experience: yes. Can we test that?

rfourquet · 2017-07-12T09:13:03Z

base/iterators.jl

+
+function iteratorsize(::Type{Flatten{I}}) where {I}
+    if isleaftype(eltype(I))
+        flatten_iteratorsize(iteratorsize(I), eltype(I)) # eltype is always defined


With this, you seem to prevent have HasLength for non-concrete numbers, e.g. Union{Int,UInt}[1, 0x2]. Why not move this test to flatten_iteratorsize for tuples, and having simply

iteratorsize(::Type{Flatten{I}}) where {I} = flatten_iteratorsize(iteratorsize(I), eltype(I))

? IOW, similar to what you did for flatten_length.

Yes, this would be better.

rfourquet · 2017-07-12T09:13:50Z

test/iterators.jl

 @test collect(flatten(Any[flatten(Any[1:2, 6:5]), flatten(Any[6:7, 8:9])])) == Any[1,2,6,7,8,9]
 @test collect(flatten(Any[2:1])) == Any[]
 @test eltype(flatten(UnitRange{Int8}[1:2, 3:4])) == Int8
+@test length(flatten(zip(1:3, 4:6))) == 6


you could add a test for numbers too

rfourquet · 2017-07-21T11:44:41Z

base/iterators.jl

+        throw(ArgumentError(
+            "Cannot compute length of a tuple-type which is not a leaf-type"))
+    end
+    nfields(T)*length(f.it)


it seems that nfields was deprecated it favor of fieldcount

this shouldn't have passed tests then. is this covered and running?

As far as I understand, this code path is tested. @mschauer do you know why this was not noticed by CI? (did the change happened after CI was run?)

I think CI picked up the change, but I did not pick it up (locally on my machine a test regarding output format of arrays is broken recently).

rfourquet · 2017-07-21T11:54:01Z

LGTM. Just one question: you are testing tuples with isleaftype, to handle the case where the eltype is an NTuple which doesn't have a fixed number of elements. Is there another case than NTuple which doesn't have a fixed number of elements? otherwise, you could dispatch on NTuple instead, and allow non-leaf-types tuples which have a fixed length (for e.g. flatten(Tuple{Integer}[(1,), (3,)])) to benefit from your work.

mschauer · 2017-07-23T13:56:10Z

Mixed tuples are not NTuples, for this reason I went with the test for leaftype. NTuples which are non-leaf-types could be covered additionally.

mschauer · 2017-07-23T20:16:22Z

Squashed and rebased.

tkelman · 2017-07-23T21:19:21Z

base/iterators.jl

+iteratorsize(::Type{Flatten{I}}) where {I} = flatten_iteratorsize(iteratorsize(I), eltype(I))
+
+function flatten_length(f, ::Type{T}) where {T<:Tuple}
+    if !isleaftype(T)


it's not very intuitive that isleaftype is the right predicate for this - are Vararg and nesting coupled to this?

rfourquet

I will merge tomorrow if no-one objects. Finer handling of tuples can be added later if needed. Thanks @mschauer !

tkelman · 2017-07-24T12:57:56Z

hold on at least until there's a good answer for the question above. is this correct even for Tuples with Vararg or nested tuples?

mschauer · 2017-07-25T19:53:30Z

it's not very intuitive that isleaftype is the right predicate for this - are Vararg and nesting coupled to this?

If a tuple type T is a leaftype, it can have instances t::T. For the instances
length(t) == nfields(typeof(t)) so length is type constant.

rfourquet · 2017-07-27T07:50:17Z

@tkelman good to go now W.R.T. the isleaftype question?

rfourquet · 2017-08-03T07:31:29Z

One CI failure is a timeout, the other seems unrelated.

mschauer mentioned this pull request Jul 6, 2017

Give Flatten-iterator HasLength() in some cases #16680

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nalimilan reviewed Jul 6, 2017

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Sacha0 reviewed Jul 6, 2017

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ararslan added the collections Data structures holding multiple items, e.g. sets label Jul 6, 2017

rfourquet reviewed Jul 7, 2017

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mschauer force-pushed the flatten2 branch from f3081d2 to e2d25fa Compare July 7, 2017 11:16

mschauer mentioned this pull request Jul 11, 2017

Iteratorsize for partition iterator #16552

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rfourquet reviewed Jul 12, 2017

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mschauer force-pushed the flatten2 branch from e2d25fa to dde472e Compare July 19, 2017 09:15

rfourquet reviewed Jul 21, 2017

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HasLength trait for some Flatten iterators

30536b8

mschauer force-pushed the flatten2 branch from dde472e to 30536b8 Compare July 23, 2017 18:20

tkelman reviewed Jul 23, 2017

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rfourquet approved these changes Jul 24, 2017

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rfourquet merged commit 5e32423 into JuliaLang:master Aug 3, 2017

tkoolen mentioned this pull request Aug 24, 2017

HasLength for even more Flatten iterators #23431

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mschauer commented Jul 6, 2017

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rfourquet commented Jul 21, 2017

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