# Type Reconstruction Question

**URL:** https://discourse.julialang.org/t/type-reconstruction-question/23092
**Category:** General Usage
**Created:** [April 12, 2019, 6:38pm UTC](https://discourse.julialang.org/t/type-reconstruction-question/23092 "2019-04-12T18:38:40Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![mauro3](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mauro3/32/292_2.png) [@mauro3](https://discourse.julialang.org/u/mauro3)
#### Post date: [April 12, 2019, 6:44pm UTC](https://discourse.julialang.org/t/type-reconstruction-question/23092/2 "2019-04-12T18:44:08Z")

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I think this is the same as was just asked:

> [@Tricky parametric type dispatch](https://discourse.julialang.org/t/tricky-parametric-type-dispatch/23064):
>
> I would like to dispatch a method like this, where T gets the type \<: AbstractParticles and the type parameters end up in F and NT. function Base.union(p1::T{F,NT},p2::S{F,NS}) where T \<: AbstractParticles where S \<: AbstractParticles{F,NS} where F where NT where NS T{F,NT+NS}([p1.particles; p2.particles]) end This does not work and an error TypeError: in Type{...} expression, expected UnionAll, got TypeVar occurs. The following definition is accepted, but it makes T include the type par…

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