# Unassigned type parameters in \`UnionAll\` of \`Tuple\` do not refer to concrete types in edge cases

**URL:** <https://discourse.julialang.org/t/unassigned-type-parameters-in-unionall-of-tuple-do-not-refer-to-concrete-types-in-edge-cases/125217>\
**Category:** General Usage\
**Tags:** type, tuple, parametric-types, diagonal-rule\
**Created:** [January 26, 2025, 7:02am UTC](https://discourse.julialang.org/t/unassigned-type-parameters-in-unionall-of-tuple-do-not-refer-to-concrete-types-in-edge-cases/125217 "2025-01-26T07:02:36Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![nsajko](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nsajko/32/221187_2.png) [@nsajko](https://discourse.julialang.org/u/nsajko)\
**Post date:** [January 29, 2025, 3:20am UTC](https://discourse.julialang.org/t/unassigned-type-parameters-in-unionall-of-tuple-do-not-refer-to-concrete-types-in-edge-cases/125217/5 "2025-01-29T03:20:00Z")

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> [@frankwswang](#):
>
> If there isn’t some implementation obstacle, I don’t see why we can’t lift off the diagonal-type rule for `T` even when `S` is assigned a concrete type.

I think it may be way too late for making that change, as explained here [PSA: Julia is not at that stage of development anymore](https://discourse.julialang.org/t/psa-julia-is-not-at-that-stage-of-development-anymore/44872).

If you really want to make this change, you could make a PR. Assuming it passes the Julia test suite, it could be further evaluated with PkgEval, to see which registered packages’ test suites does it break. Hypothetically it could get accepted as a _minor change_ if it’s not too breaking, however I think you’d have to present a stronger motivation than given here.

It might be interesting to see what would such a PR break in the ecosystem 😂

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