Allow AbstractUnitRange for string getindex

[mkitti]

Several methods could be generalized to work with AbstractUnitRange rather than just UnitRange. There are now several AbstractUnitRange subtypes:

julia> subtypes(AbstractUnitRange)
4-element Vector{Any}:
 Base.IdentityUnitRange
 Base.OneTo
 Base.Slice
 UnitRange

This pull request allows AbstractUnitRange for getindex on a String.

There seem to be some ambiguous method errors associated with the current change.

[vtjnash]

There seem to be some ambiguous method errors

Looks like another method signature update, that was also simply too strict previously, is needed here

julia/base/strings/substring.jl

Line 255 in 5ff9e3a

getindex(s::AbstractString, r::UnitRange{<:Integer}) = SubString(s, r)

[timholy]

What does s[OffsetArray(1:3, -1:1)] do? I guess that's technically not a range, but nothing prevents me from writing one whose values start at 1 but whose indices start at something that String can't support. E.g,

julia> r = OffsetArrays.IdOffsetRange(3:5, -2)
OffsetArrays.IdOffsetRange(values=1:3, indices=-1:1)

julia> r isa AbstractUnitRange
true

julia> first(r)
1

julia> firstindex(r)
-1

See https://juliaarrays.github.io/OffsetArrays.jl/stable/internals/#The-axes-of-OffsetArrays and the "fundamental axiom of generalized indexing."

Easy fix: add a Base.require_one_based_indexing(r).

[mkitti]

What does s[OffsetArray(1:3, -1:1)] do?

The first question should be, "what did it do?". Here's the behavior on Julia 1.6.0:

julia> VERSION
v"1.6.0"

julia> using OffsetArrays

julia> s = "Tim Holy"
"Tim Holy"

julia> r = OffsetArrays.IdOffsetRange(3:5, -2)
OffsetArrays.IdOffsetRange(values=1:3, indices=-1:1)

julia> s[r]
"Tim"

julia> s[OffsetArray(1:3, -1:1)]
"Tim"

julia> @which s[r]
getindex(s::AbstractString, v::AbstractVector{var"#s79"} where var"#s79"<:Integer) in Base at strings/basic.jl:192

julia> Base.getindex(s::String, r::AbstractUnitRange{<:Integer}) = s[Int(first(r)):Int(last(r))]

julia> s[r]
"Tim"

julia> @which s[r]
getindex(s::String, r::AbstractUnitRange{var"#s1"} where var"#s1"<:Integer) in Main at REPL[11]:1

[timholy]

Interesting! A bit unexpected, but I guess there is an argument for strings that simply says they don't pay attention to the indexes of the indexes, but only to the values. 👍

[mkitti]

@timholy you may also be interested in #39241 (comment) (merged),
#41805, #41809, and #41810 (approved by @vtjnash, pending merge)

[vtjnash]

Strings also don't pay attention to the values either, just the end points. They don't really act like arrays when indexed.