# Silent type promotion when creating range using \`a🅱c\`

**URL:** <https://discourse.julialang.org/t/silent-type-promotion-when-creating-range-using-ac/127671>\
**Category:** General Usage\
**Created:** [April 3, 2025, 12:34pm UTC](https://discourse.julialang.org/t/silent-type-promotion-when-creating-range-using-ac/127671 "2025-04-03T12:34:10Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [April 3, 2025, 2:23pm UTC](https://discourse.julialang.org/t/silent-type-promotion-when-creating-range-using-ac/127671/2 "2025-04-03T14:23:12Z")

</div>

What’s happening is more explicit with `Float64`:

```julia-repl
julia> typeof(0:0.1:1)
StepRangeLen{Float64, Base.TwicePrecision{Float64}, Base.TwicePrecision{Float64}, Int64}

```

It’s a design choice, and certainly a debatable one at that. It’s done to avoid roundoff issues. Compare

```julia
julia> collect(0:0.1:1)
11-element Vector{Float64}:
 0.0
 0.1
 0.2
 0.3
 0.4
 0.5
 0.6
 0.7
 0.8
 0.9
 1.0

julia> collect(StepRangeLen(0,0.1,11))
11-element Vector{Float64}:
 0.0
 0.1
 0.2
 0.30000000000000004
 0.4
 0.5
 0.6000000000000001
 0.7000000000000001
 0.8
 0.9
 1.0

```

This issue _appears_ cosmetic, but it can actually lead to significant ambiguity. Knowing that `0.1*3 == 0.30000000000000004 > 0.3`, should `last(0.0:0.1:0.3)` be `2.0`, `3.0`, or `0.30000000000000004`? The `TwicePrecision` step is the only way to give the user what they (usually) want while maintaining consistency.

But I will sympathize that I, too, find it a tedious to have to use the `StepRangeLen` constructor when I’m okay with a lower precision step. Especially because there is a [performance cost](https://discourse.julialang.org/t/confusion-on-performance-when-using-the-broadcasting-macro-vs-explicit-operators/127380/7).

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