# Brackets on structures Julia

**URL:** <https://discourse.julialang.org/t/brackets-on-structures-julia/73532>\
**Category:** Performance\
**Tags:** parametric-types, struct\
**Created:** [December 23, 2021, 1:51pm UTC](https://discourse.julialang.org/t/brackets-on-structures-julia/73532 "2021-12-23T13:51:30Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Leticia-maria](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/leticia-maria/32/30981_2.png) [@Leticia-maria](https://discourse.julialang.org/u/Leticia-maria)\
**Post date:** [December 23, 2021, 1:51pm UTC](https://discourse.julialang.org/t/brackets-on-structures-julia/73532/1 "2021-12-23T13:51:30Z")

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what means this brackets on struct?:

```julia
struct Graph{T}
    adjacency_lists :: Dict{T, Set{T}}
    edge_weights :: Dict{Tuple{T, T}, Float64}
end

```

---

<div class="post-metadata">

**Author:** ![John\_Gibson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/john_gibson/32/5321_2.png) [@John\_Gibson](https://discourse.julialang.org/u/John_Gibson)\
**Post date:** [December 23, 2021, 2:17pm UTC](https://discourse.julialang.org/t/brackets-on-structures-julia/73532/2 "2021-12-23T14:17:12Z")

</div>

The bracketed `T` is a parametrized type. E.g. the `Graph` type can be a `Graph{Int64}` or `Graph{Float64}` or whatever. See [Types · The Julia Language](https://docs.julialang.org/en/v1/manual/types/#Parametric-Types)