# Broadcasting and pairs using \`.=\>\`

**URL:** <https://discourse.julialang.org/t/broadcasting-and-pairs-using/24739>\
**Category:** General Usage\
**Created:** [May 29, 2019, 3:39pm UTC](https://discourse.julialang.org/t/broadcasting-and-pairs-using/24739 "2019-05-29T15:39:30Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [May 29, 2019, 3:39pm UTC](https://discourse.julialang.org/t/broadcasting-and-pairs-using/24739/1 "2019-05-29T15:39:30Z")

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In `replace` a pair is used to specify a pattern and its replacement, as in `replace("123", "2" => "two")`. When broadcasting, the following won’t work (as expected) as a pair is iterable: `replace.(["123", "246"], "2"=>"two")`. The solution is to wrap the pair into a length-1 container or use `Ref`, as with `replace.(["123", "246"], Ref("2"=>"two"))`. Okay, but this syntax also works: `replace.(["123", "246"], "2" .=> "two")`. My question, is this by design and expected behaviour or may it be changed in the future? I personally like it, though can’t explain to myself why exactly it works.

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**Author:** ![mbauman](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mbauman/32/31082_2.png) [@mbauman](https://discourse.julialang.org/u/mbauman)\
**Post date:** [May 29, 2019, 3:56pm UTC](https://discourse.julialang.org/t/broadcasting-and-pairs-using/24739/2 "2019-05-29T15:56:10Z")

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Yes, this is by design — what’s happening is that strings broadcast like scalars. And broadcasting over two scalars is completely supported. The only thing you need to consider is that broadcasted operators end up “on the inside” of the fused `for` loop, and will repeatedly be evaluated for each iteration. In this case, I’m quite certain it’ll essentially be a no-op, but you might have a more expensive function or a function with side-effects (like `rand.()` vs `rand()`) in which case there will be more dramatic effects.

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**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [May 29, 2019, 3:56pm UTC](https://discourse.julialang.org/t/broadcasting-and-pairs-using/24739/3 "2019-05-29T15:56:21Z")

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> [@j\_verzani](#):
>
> My question, is this by design and expected behaviour

Sure! There’s nothing special about `=>` ; it’s just a shorthand for `Pair`. So your example can also be written as:

```julia
julia> replace.(["123", "246"], Pair.("2", "two"))
2-element Array{String,1}:
 "1two3"
 "two46"

```

Fore more on why that works, see [More Dots: Syntactic Loop Fusion in Julia](https://julialang.org/blog/2017/01/moredots)

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**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [May 29, 2019, 4:06pm UTC](https://discourse.julialang.org/t/broadcasting-and-pairs-using/24739/4 "2019-05-29T16:06:08Z")

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Thanks. The thing that caught me was `Pair.("2", "two")` evaluates to `"2" => "two"` so got confused forgetting the pass happens at the syntax level, not after evaluation. Thanks for pointing to that blog post for the reminder.