# Cannot use parametric type within function body

**URL:** <https://discourse.julialang.org/t/cannot-use-parametric-type-within-function-body/28224>\
**Category:** New to Julia\
**Tags:** parametric-types\
**Created:** [August 30, 2019, 11:36pm UTC](https://discourse.julialang.org/t/cannot-use-parametric-type-within-function-body/28224 "2019-08-30T23:36:52Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![marius311](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marius311/32/3953_2.png) [@marius311](https://discourse.julialang.org/u/marius311)\
**Post date:** [August 31, 2019, 1:10am UTC](https://discourse.julialang.org/t/cannot-use-parametric-type-within-function-body/28224/9 "2019-08-31T01:10:48Z")

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I _think_ this is the same as: [Dispatching on the result of unwrap\_unionall seems weird?](https://discourse.julialang.org/t/dispatching-on-the-result-of-unwrap-unionall-seems-weird/25677) (which gives an even more MWE).

I’m no type-system expert, but to me it still kind of seems like a bug, e.g. in OPs first example, how can `T` simultaneously be undefined but also have been verified to be `T<:Real` ?

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_[View the full topic](https://discourse.julialang.org/t/cannot-use-parametric-type-within-function-body/28224)._