make [a, b] not concatenate

[SamChill]

This works:

julia> [ 1:3, 4 ]
4-element Int64 Array:
 1
 2
 3
 4

and this works:

julia> Uint8[ 1:3 ]
3-element Uint8 Array:
 0x01
 0x02
 0x03

but this doesn't:

julia> Uint8[ 1:3, 4]
ERROR: no method convert(Type{Uint8},Range1{Int64})
 in setindex! at array.jl:392
 in getindex at array.jl:161

Is this expected behavior? I would expect to be able to construct Uint8 arrays this way.

[simonster]

If you specify the type of an array when constructing it, Julia doesn't attempt to vcat its elements. Your code won't work for Int64 either:

julia> Int64[1:3, 4]
ERROR: no method convert(Type{Int64},Range1{Int64})
 in setindex! at array.jl:403
 in getindex at array.jl:163

I think you want

julia> [uint8(1):uint8(3), uint8(4)]
4-element Uint8 Array:
 0x01
 0x02
 0x03
 0x04

[JeffBezanson]

It was supposed to be the case that T[x, y, z] made an array of element type T, so x, y, and z would each be converted to type T, and indeed you can't convert an integer range to type Uint8. Note that convert is very specific in this sense; converting to Uint8 means getting a Uint8 back, not an array of Uint8 or a range of Uint8 etc.

Then the waters were muddied a bit by the definition (array.jl:173) that allows Int[1:3]. I probably allowed that change at the time, and I deeply regret it. You would think constructing an array with a certain element type would be a simple enough matter.

We could go farther down this road and allow T[...] for all concatenations, but actually I'd prefer to remove all concatenating behavior from [] except for [a b] and [a; b] etc.

[StefanKarpinski]

We could go farther down this road and allow T[...] for all concatenations, but actually I'd prefer to remove all concatenating behavior from [] except for [a b] and [a; b] etc.

I still think this is probably a good idea. It would expand and clarify the distinction between [x,y,z] and [x y z].

[toivoh]

+1

[ViralBShah]

I would actually love to remove all concatenating behaviour apart for [a b] and [a; b] too. I think this is one syntax choice in our design that is inelegant.

[JeffBezanson]

It appears to be unanimous!
Unfortunately it will be really hard to track down all uses of [a,b] that rely on concatenation.

[toivoh]

Deprecation warnings for concatenation could be a good start at least.

[StefanKarpinski]

We can turn them into a call to vcat_deprecated and print a warning. At some point we'll have eliminated all such calls and we can change the behavior to straight up fail and/or just not concatenate.

[mlubin]

What's the replacement for concatenating vcat?

[mlubin]

And how does this fix the issue:

julia> Uint8[1:3;4]
ERROR: no method convert(Type{Uint8},Range1{Int64})
 in setindex! at array.jl:415
 in getindex at array.jl:163

[StefanKarpinski]

I would allow Uint8[1:3;4] to do concatenation while Uint[1:3,4] would fail because 1:3 can't be converted to a Uint8. So it doesn't fix this issue without further changes, but makes it sane to do those changes.

[JeffBezanson]

And the question is whether Uint8[1:3] has zero commas or zero semicolons :)

[StefanKarpinski]

Ah yes, that is an issue too. Drat.

[JeffBezanson]

Color me amazed that the idea of making Uint8[x] always return a 1-element Uint8 array is so contentious.