JuliaLang/julia

Support `convert(AbstractArray{T}, ::AbstractRange)` and variants

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#27,138 opened on May 17, 2018

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 (0 comments) (6 reactions) (0 assignees)Julia (5,773 forks)batch import
arrayshelp wanted

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Description

I'm surprised that converting the type of a range constructs a dense vector:

julia> AbstractVector{Float64}(1:10)
10-element Array{Float64,1}:
  1.0
  2.0
  3.0
  4.0
  5.0
  6.0
  7.0
  8.0
  9.0
 10.0

julia> convert(AbstractVector{Float64},1:10)
10-element Array{Float64,1}:
  1.0
  2.0
  3.0
  4.0
  5.0
  6.0
  7.0
  8.0
  9.0
 10.0

julia> convert(AbstractRange{Float64},1:10)
ERROR: MethodError: no method matching AbstractRange{Float64}(::UnitRange{Int64})
Closest candidates are:
  AbstractRange{Float64}(::Any) where T<:AbstractArray at abstractarray.jl:22
Stacktrace:
 [1] Type at ./abstractarray.jl:22 [inlined]
 [2] convert(::Type{AbstractRange{Float64}}, ::UnitRange{Int64}) at ./range.jl:100
 [3] top-level scope

I would expect all of the above to return 1.0:1.0:10.0.

Contributor guide

Research direction
Examine the convert method for AbstractRange in range.jl and the Type constructor in abstractarray.jl to understand why conversion of a range to AbstractRange fails and why conversion to AbstractVector materializes. Consider adding a convert method that preserves the range structure.
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