# Trouble defining \`broadcast\` method between custom array type and \`Number\`

**URL:** <https://discourse.julialang.org/t/trouble-defining-broadcast-method-between-custom-array-type-and-number/3643>\
**Category:** General Usage\
**Created:** [May 11, 2017, 8:01am UTC](https://discourse.julialang.org/t/trouble-defining-broadcast-method-between-custom-array-type-and-number/3643 "2017-05-11T08:01:59Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![ssfrr](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ssfrr/32/3736_2.png) [@ssfrr](https://discourse.julialang.org/u/ssfrr)\
**Post date:** [May 11, 2017, 8:01am UTC](https://discourse.julialang.org/t/trouble-defining-broadcast-method-between-custom-array-type-and-number/3643/1 "2017-05-11T08:01:59Z")

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Consider the following type definition for a custom array type (using 0.6.0-rc1):

```julia
struct MyArr{T, N} <: AbstractArray{T, N}
    x::Array{T, N}
end

Base.size(A::MyArr) = size(A.x)
Base.IndexStyle(::Type{T}) where {T <: MyArr} = Base.IndexLinear()
Base.getindex(A::MyArr, I...) = getindex(A.x, I...)
Base.broadcast(op, A::MyArr, other) = MyArr(broadcast(op, A.x, other))
Base.broadcast(op, other, A::MyArr) = MyArr(broadcast(op, other, A.x))

a = MyArr(rand(4))

```

The idea being that I want the result of a broadcast to be wrapped in a `MyArr`.

This works fine if I broadcast a `MyArr` with a `Vector` (`a .+ rand(4)`), but if I try `a .+ 1.0` I get a standard `Vector`. Strangely running `@which a .+ 1.0` gives me `deprecated.jl:339`, which seems to print a depwarn and call `broadcast`, but I don’t see the depwarn and when I call `broadcast(+, a, 1.0)` I get a wrapped `MyArr` as expected.

Not sure if this is a bug or I just need to do some more method magic to properly handle `broadcast`s on `Numbers`

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<div class="post-metadata">

**Author:** ![mbauman](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mbauman/32/31082_2.png) [@mbauman](https://discourse.julialang.org/u/mbauman)\
**Post date:** [May 11, 2017, 3:33pm UTC](https://discourse.julialang.org/t/trouble-defining-broadcast-method-between-custom-array-type-and-number/3643/2 "2017-05-11T15:33:59Z")

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Broadcasting with literals lowers to `broadcast(x->x+1.0, a)`. The solution is to hook into broadcast’s output array selection algorithm. I still haven’t bothered to figure out all the details, but check out `Base.Broadcast.containertype`.

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<div class="post-metadata">

**Author:** ![ssfrr](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ssfrr/32/3736_2.png) [@ssfrr](https://discourse.julialang.org/u/ssfrr)\
**Post date:** [May 11, 2017, 4:01pm UTC](https://discourse.julialang.org/t/trouble-defining-broadcast-method-between-custom-array-type-and-number/3643/3 "2017-05-11T16:01:13Z")

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Thanks! I had a hunch if was some kind of lowering thing but didn’t know where to look.

I’ll look into it and report back what I find.

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<div class="post-metadata">

**Author:** ![ssfrr](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ssfrr/32/3736_2.png) [@ssfrr](https://discourse.julialang.org/u/ssfrr)\
**Post date:** [May 11, 2017, 5:08pm UTC](https://discourse.julialang.org/t/trouble-defining-broadcast-method-between-custom-array-type-and-number/3643/4 "2017-05-11T17:08:42Z")

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So I ended up just defining:

```julia
Base.broadcast(op, A::MyArr) = MyArr(broadcast(op, A.x))

```

And that picked up the case that was being missed. I’m not sure if that’s the Right Way but it seems to pass my tests.