allow `getindex(::MyType, ::Colon)` to be customized

[rfourquet]

And similarly for setindex!.
For example:

type A end
Base.getindex(a::A, ::Range) = 0
Base.getindex(a::A, ::Colon) = 1

julia> A()[:]
ERROR: `endof` has no method matching endof(::A)

This is worse if endof(::A) is defined, as then A()[:] chooses silently the unintended getindex method.

If allowing customization of Base.getindex(a::A, ::Colon) does not happen, I would request that a[:] is translated to a[beginof(a):endof(a)], as some indexable collections have an indice starting at something else than 1.

At the very least, the doc for getindex/setindex! should mention this special case, where "The syntax a[i,j,...] is converted by the compiler to getindex(a, i, j, ...)" does not seem true.

Also, in "base/subarray.jl", this method is defined: getindex{T}(v::AbstractArray{T,1}, ::Colon) = v, should it be removed or is it used?

[timholy]

This is something that needs to be changed in the parser, and is part of #9150.

Re the getindex method in base/subarray.jl, I suspect it's there currently just to resolve a method ambiguity. But someday it will be directly useful.

[mlubin]

👍
This is essential for proper slicing semantics of non-one-based arrays that are commonly used in JuMP.

[jakebolewski]

I have a branch that already does this, has @andreasnoack not included it in #9150?

[andreasnoack]

Yes. It is part of #9150 which I'll hopefully will finalize between Christmas and the end of the year.

[rfourquet]

Oh I had seen #9150 before posting, but didn't understand it did hat I wanted, good!