# Composite types and their subtypes
**URL:** https://discourse.julialang.org/t/composite-types-and-their-subtypes/38371
**Category:** New to Julia
**Tags:** question
**Created:** [April 28, 2020, 1:25pm UTC](https://discourse.julialang.org/t/composite-types-and-their-subtypes/38371 "2020-04-28T13:25:33Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@markmbaum](https://discourse.julialang.org/u/markmbaum)
#### Post date: [April 28, 2020, 1:25pm UTC](https://discourse.julialang.org/t/composite-types-and-their-subtypes/38371/1 "2020-04-28T13:25:33Z")
I’m still getting used to the type system in Julia. Is the following composite type,
```julia
mutable struct Point{Float64}
x
y
end
```
equivalent to
```julia
mutable struct Point
x::Float64
y::Float64
end
```
It seems like the answer is no?
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [April 28, 2020, 1:46pm UTC](https://discourse.julialang.org/t/composite-types-and-their-subtypes/38371/2 "2020-04-28T13:46:32Z")
You’re correct that the answer is no. See: [Types · The Julia Language](https://docs.julialang.org/en/v1/manual/types/#Parametric-Types-1)
Your first type has a type parameter with the name `Float64` which does absolutely nothing. The fields `x` and `y` can still be of any type. Moreover, the fact that the type parameter has a name which is the same as an existing type (`Float64`) is totally irrelevant.
Your second type, on the other hand, actually restricts the `x` and `y` fields to be of type `Float64`.
To implement a parametric `Point` type, you want something like this:
```julia
mutable struct Point{T}
x::T
y::T
end
```
which creates a struct with a parameter named `T` and two fields which must both be of that same type `T`.