Implement Base.broadcastable for BioSequence types.

Author: Ben J. Ward

src/biosequence/biosequence.jl

@@ -157,3 +157,4 @@ include("printing.jl")
 include("transformations.jl")
 include("counting.jl")
 include("copying.jl")
+include("seqbroadcast.jl")

src/biosequence/seqbroadcast.jl

@@ -0,0 +1,269 @@
+###
+### Broadcasting with BioSequences.
+###
+### Customising the broadcasting machinery for BioSequences.
+###
+### This file is a part of BioJulia.
+### License is MIT: https://github.com/BioJulia/BioSequences.jl/blob/master/LICENSE.md
+
+
+# First we ensure that BioSequence types are actually passed to the broadcast
+# machinery.
+# 
+# By default, this would otherwise `collect` the sequence into a `Vector` of
+# `DNA` or `RNA` etc. This wastes time and memory, when broadcasting should
+# just be able to use the BioSequence itself as if it were an array with a
+# a single dimension, akin to Vector.
+Base.broadcastable(x::BioSequence) = x
+
+
+
+#=
+
+Let's have a look at the example of broadcasting addition with a vector.
+
+@less broadcast(+, [1,2,3], 1)
+===
+broadcast(f::Tf, As...) where {Tf} = materialize(broadcasted(f, As...))
+
+
+@less Base.broadcasted(+, [1,2,3], 1)
+===
+@inline function broadcasted(f, arg1, arg2, args...)
+    arg1′ = broadcastable(arg1)
+    arg2′ = broadcastable(arg2)
+    args′ = map(broadcastable, args)
+    broadcasted(combine_styles(arg1′, arg2′, args′...), f, arg1′, arg2′, args′...)
+end
+@inline broadcasted(::S, f, args...) where S<:BroadcastStyle = Broadcasted{S}(f, args)
+
+bc =  Base.broadcasted(Base.Broadcast.combine_styles(arg1, arg2), +, arg1, arg2)
+Base.Broadcast.Broadcasted(+, ([1, 2, 3], 1))
+
+typeof(bc)
+Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1}, Nothing, typeof(+), Tuple{Vector{Int64}, Int64}}
+
+
+@less Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1}}(+, (arg1, arg2))
+===
+function Broadcasted{Style}(f::F, args::Args, axes=nothing) where {Style, F, Args<:Tuple}
+    # using Core.Typeof rather than F preserves inferrability when f is a type
+    Broadcasted{Style, typeof(axes), Core.Typeof(f), Args}(f, args, axes)
+end
+
+
+@less materialize(bc)
+===
+@inline materialize(bc::Broadcasted) = copy(instantiate(bc))
+materialize(x) = x
+
+
+@less Base.Broadcast.instantiate(bc)
+===
+@inline function instantiate(bc::Broadcasted{Style}) where {Style}
+    if bc.axes isa Nothing # Not done via dispatch to make it easier to extend instantiate(::Broadcasted{Style})
+        axes = combine_axes(bc.args...)
+    else
+        axes = bc.axes
+        check_broadcast_axes(axes, bc.args...)
+    end
+    return Broadcasted{Style}(bc.f, bc.args, axes)
+end
+
+
+@less Base.Broadcast.combine_axes(bc.args...)
+===
+@inline combine_axes(A, B...) = broadcast_shape(axes(A), combine_axes(B...))
+@inline combine_axes(A, B) = broadcast_shape(axes(A), axes(B))
+
+
+@less @less Base.Broadcast.broadcast_shape(axes([1,2,3]), axes(1))
+===
+broadcast_shape(shape::Tuple) = shape
+broadcast_shape(shape::Tuple, shape1::Tuple, shapes::Tuple...) = broadcast_shape(_bcs(shape, shape1), shapes...)
+
+
+@less Base.Broadcast._bcs(axes([1,2,3]), axes(1))
+===
+_bcs(shape::Tuple, ::Tuple{}) = (shape[1], _bcs(tail(shape), ())...)
+
+_bcs consolidates two shapes into a single output shape
+
+shape = axes([1,2,3])
+@less Base.Broadcast._bcs(Base.tail(shape), ())
+===
+_bcs(::Tuple{}, ::Tuple{}) = ()
+()
+
+(shape[1], _bcs(tail(shape), ())...)
+
+
+@less copy(Base.Broadcast.instantiate(bc))
+===
+@inline function copy(bc::Broadcasted{Style}) where {Style}
+    ElType = combine_eltypes(bc.f, bc.args)
+    if Base.isconcretetype(ElType)
+        # We can trust it and defer to the simpler `copyto!`
+        return copyto!(similar(bc, ElType), bc)
+    end
+    # When ElType is not concrete, use narrowing. Use the first output
+    # value to determine the starting output eltype; copyto_nonleaf!
+    # will widen `dest` as needed to accommodate later values.
+    bc′ = preprocess(nothing, bc)
+    iter = eachindex(bc′)
+    y = iterate(iter)
+    if y === nothing
+        # if empty, take the ElType at face value
+        return similar(bc′, ElType)
+    end
+    # Initialize using the first value
+    I, state = y
+    @inbounds val = bc′[I]
+    dest = similar(bc′, typeof(val))
+    @inbounds dest[I] = val
+    # Now handle the remaining values
+    # The typeassert gives inference a helping hand on the element type and dimensionality
+    # (work-around for #28382)
+    ElType′ = ElType === Union{} ? Any : ElType <: Type ? Type : ElType
+    RT = dest isa AbstractArray ? AbstractArray{<:ElType′, ndims(dest)} : Any
+    return copyto_nonleaf!(dest, bc′, iter, state, 1)::RT
+end
+
+
+@less Base.Broadcast.combine_eltypes(bc.f, bc.args)
+===
+combine_eltypes(f, args::Tuple) = promote_typejoin_union(Base._return_type(f, eltypes(args)))
+
+@less Base.Broadcast.eltypes(bc.args)
+
+@less Base._return_type(+, Base.Broadcast.eltypes(bc.args))
+
+@less Base.Broadcast.promote_typejoin_union(Base._return_type(+, Base.Broadcast.eltypes(bc.args)))
+===
+function promote_typejoin_union(::Type{T}) where T
+    if T === Union{}
+        return Union{}
+    elseif T isa UnionAll
+        return Any # TODO: compute more precise bounds
+    elseif T isa Union
+        return promote_typejoin(promote_typejoin_union(T.a), promote_typejoin_union(T.b))
+    elseif T <: Tuple
+        return typejoin_union_tuple(T)
+    else
+        return T
+    end
+end
+
+
+@less similar(bc, Base.Broadcast.combine_eltypes(bc.f, bc.args))
+===
+Base.similar(bc::Broadcasted, ::Type{T}) where {T} = similar(bc, T, axes(bc))
+Base.similar(::Broadcasted{DefaultArrayStyle{N}}, ::Type{ElType}, dims) where {N,ElType} = similar(Array{ElType}, dims)
+Base.similar(::Broadcasted{DefaultArrayStyle{N}}, ::Type{Bool}, dims) where N = similar(BitArray, dims)
+
+@less copyto!(similar(bc, Base.Broadcast.combine_eltypes(bc.f, bc.args)), bc)
+===
+## general `copyto!` methods
+# The most general method falls back to a method that replaces Style->Nothing
+# This permits specialization on typeof(dest) without introducing ambiguities
+@inline copyto!(dest::AbstractArray, bc::Broadcasted) = copyto!(dest, convert(Broadcasted{Nothing}, bc))
+
+
+@less copyto!(dest, convert(Base.Broadcast.Broadcasted{Nothing}, bc))
+===
+@inline function copyto!(dest::AbstractArray, bc::Broadcasted{Nothing})
+    axes(dest) == axes(bc) || throwdm(axes(dest), axes(bc))
+    # Performance optimization: broadcast!(identity, dest, A) is equivalent to copyto!(dest, A) if indices match
+    if bc.f === identity && bc.args isa Tuple{AbstractArray} # only a single input argument to broadcast!
+        A = bc.args[1]
+        if axes(dest) == axes(A)
+            return copyto!(dest, A)
+        end
+    end
+    bc′ = preprocess(dest, bc)
+    # Performance may vary depending on whether `@inbounds` is placed outside the
+    # for loop or not. (cf. https://github.com/JuliaLang/julia/issues/38086)
+    @inbounds @simd for I in eachindex(bc′)
+        dest[I] = bc′[I]
+    end
+    return dest
+end
+
+
+@less Base.Broadcast.preprocess(dest, bc)
+===
+# Preprocessing a `Broadcasted` does two things:
+# * unaliases any arguments from `dest`
+# * "extrudes" the arguments where it is advantageous to pre-compute the broadcasted indices
+@inline preprocess(dest, bc::Broadcasted{Style}) where {Style} = Broadcasted{Style}(bc.f, preprocess_args(dest, bc.args), bc.axes)
+preprocess(dest, x) = extrude(broadcast_unalias(dest, x))
+
+@inline preprocess_args(dest, args::Tuple) = (preprocess(dest, args[1]), preprocess_args(dest, tail(args))...)
+preprocess_args(dest, args::Tuple{Any}) = (preprocess(dest, args[1]),)
+preprocess_args(dest, args::Tuple{}) = ()
+
+
+Base.Broadcast.preprocess(dest, bc.args[1])
+@less Base.Broadcast.broadcast_unalias(dest, bc.args[1])
+===
+# For broadcasted assignments like `broadcast!(f, A, ..., A, ...)`, where `A`
+# appears on both the LHS and the RHS of the `.=`, then we know we're only
+# going to make one pass through the array, and even though `A` is aliasing
+# against itself, the mutations won't affect the result as the indices on the
+# LHS and RHS will always match. This is not true in general, but with the `.op=`
+# syntax it's fairly common for an argument to be `===` a source.
+broadcast_unalias(dest, src) = dest === src ? src : unalias(dest, src)
+broadcast_unalias(::Nothing, src) = src
+
+
+@less Base.Broadcast.unalias(dest, bc.args[1])
+===
+## rudimentary aliasing detection ##
+"""
+    Base.unalias(dest, A)
+
+Return either `A` or a copy of `A` in a rough effort to prevent modifications to `dest` from
+affecting the returned object. No guarantees are provided.
+
+Custom arrays that wrap or use fields containing arrays that might alias against other
+external objects should provide a [`Base.dataids`](@ref) implementation.
+
+This function must return an object of exactly the same type as `A` for performance and type
+stability. Mutable custom arrays for which [`copy(A)`](@ref) is not `typeof(A)` should
+provide a [`Base.unaliascopy`](@ref) implementation.
+
+See also [`Base.mightalias`](@ref).
+"""
+unalias(dest, A::AbstractArray) = mightalias(dest, A) ? unaliascopy(A) : A
+unalias(dest, A::AbstractRange) = A
+unalias(dest, A) = A
+
+"""
+    Base.mightalias(A::AbstractArray, B::AbstractArray)
+
+Perform a conservative test to check if arrays `A` and `B` might share the same memory.
+
+By default, this simply checks if either of the arrays reference the same memory
+regions, as identified by their [`Base.dataids`](@ref).
+"""
+mightalias(A::AbstractArray, B::AbstractArray) = !isbits(A) && !isbits(B) && !_isdisjoint(dataids(A)
+, dataids(B))
+mightalias(x, y) = false
+
+"""
+    Base.dataids(A::AbstractArray)
+
+Return a tuple of `UInt`s that represent the mutable data segments of an array.
+
+Custom arrays that would like to opt-in to aliasing detection of their component
+parts can specialize this method to return the concatenation of the `dataids` of
+their component parts.  A typical definition for an array that wraps a parent is
+`Base.dataids(C::CustomArray) = dataids(C.parent)`.
+"""
+dataids(A::AbstractArray) = (UInt(objectid(A)),)
+dataids(A::Array) = (UInt(pointer(A)),)
+dataids(::AbstractRange) = ()
+dataids(x) = ()
+
+=#
+

src/longsequences/indexing.jl

@@ -69,3 +69,14 @@ end
 
 # Broadcasting
 
+#Base.axes(x::BioSymbol) = ()
+#Base.ndims(::Type{<:BioSymbol}) = 0
+#Base.ndims(x::BioSymbol) = 0
+#Base.broadcastable(x::BioSymbol) = x
+
+#Base.broadcastable(x::LongSequence) = x
+#Base.getindex(x::LongSequence, i::Base.CartesianIndex{1}) = x[first(i.I)]
+
+#Base.BroadcastStyle(::Type{T}) where {T<:LongSequence} = Broadcast.Style{T}()
+
+#Base.BroadcastStyle(::Broadcast.Style{<:LongSequence}, ::Broadcast.DefaultArrayStyle{N}) where {N} = Broadcast.DefaultArrayStyle{N}()