# \#wat

**URL:** https://discourse.julialang.org/tag/wat/1522.md

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## [Semantically equivalent expressions with wildly different performance](https://discourse.julialang.org/t/semantically-equivalent-expressions-with-wildly-different-performance/131123)

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**Author:** [@bremez](https://discourse.julialang.org/u/bremez)\
**Replies:** 10\
**Last updated:** [July 28, 2025, 2:54pm UTC](https://discourse.julialang.org/t/semantically-equivalent-expressions-with-wildly-different-performance/131123 "2025-07-28T14:54:10Z")

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I came across the following example when I needed something that beats the performance of LinearAlgebra’s build in mul!(M, x, y'). Any known reason for this huge difference in performance? Tested on 11.6. using Benchmar…

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## [Notice: a subtle footgun: UnionAll type variable order + method static parameter normalization](https://discourse.julialang.org/t/notice-a-subtle-footgun-unionall-type-variable-order-method-static-parameter-normalization/113779)

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**Author:** [@nsajko](https://discourse.julialang.org/u/nsajko)\
**Replies:** 2\
**Last updated:** [January 31, 2025, 10:12am UTC](https://discourse.julialang.org/t/notice-a-subtle-footgun-unionall-type-variable-order-method-static-parameter-normalization/113779 "2025-01-31T10:12:47Z")

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Consider this snippet: id(::Type{T}) where {T} = T some\_type{7,Int} == id(some\_type){7,Int} Naively, it seems like the comparison on the second line should return true for any type some\_type, assuming neither type appl…

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## [A most harrowing collection of Julia WATs](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323)

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**Author:** [@miguelraz](https://discourse.julialang.org/u/miguelraz)\
**Replies:** 106\
**Last updated:** [January 27, 2024, 4:05pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323 "2024-01-27T16:05:08Z")

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Hello all! :wave: I’ve been collecting a few of the most cursed corner cases of Julia WATs that I know of here (WIP), but I would appreciate if people could share their own rare specimens as well. Please ping me with y…

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## [Why is relpath("x","y") == "../x"?](https://discourse.julialang.org/t/why-is-relpath-x-y-x/107932)

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**Author:** [@evanfields](https://discourse.julialang.org/u/evanfields)\
**Replies:** 5\
**Last updated:** [December 22, 2023, 2:26pm UTC](https://discourse.julialang.org/t/why-is-relpath-x-y-x/107932 "2023-12-22T14:26:21Z")

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julia\> relpath("tatooine", "naboo") "../tatooine" The docs say relpath(path::AbstractString, startpath::AbstractString = ".") -\> AbstractString Return a relative filepath to path either from the current directory or …