# Type of type parameters
**URL:** https://discourse.julialang.org/t/type-of-type-parameters/5646
**Category:** General Usage
**Created:** [August 30, 2017, 10:08pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646 "2017-08-30T22:08:43Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@gasagna](https://discourse.julialang.org/u/gasagna)
#### Post date: [August 30, 2017, 10:08pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646/1 "2017-08-30T22:08:43Z")
Sometimes I wish I could express that the parameters of a certain parametrised struct must be of a certain type. For example, I would like to have syntax that allows
```julia
struct ContinuousShift{s::Real} <: AbstractSymmetry end
```
to mean that the parameter `s` will be a real number, or maybe
```julia
struct DiscreteShift{m::Int} <: AbstractSymmetry end
```
for when only integers would make sense. I can live without this, but I think other people might have wanted this kind of ability at some point.
---
### Author:  [@jebej](https://discourse.julialang.org/u/jebej)
#### Post date: [August 30, 2017, 10:21pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646/2 "2017-08-30T22:21:23Z")
Is this: `struct ContinuousShift{s<:Real} <: AbstractSymmetry end` not what you want?
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [August 30, 2017, 10:28pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646/3 "2017-08-30T22:28:56Z")
I agree that that syntax would be nice. The closest I’ve found is:
```julia
julia> struct Foo{N}
x::Int
Foo{N}(x) where {N} = new{typeassert(N, Integer)}(x)
end
julia> Foo{3}(1)
Foo{3}(1)
julia> Foo{3.5}(1)
ERROR: TypeError: Type: in typeassert, expected Integer, got Float64
Stacktrace:
[1] Foo{3.5}(::Int64) at ./REPL[1]:3
```
---
### Author:  [@tkoolen](https://discourse.julialang.org/u/tkoolen)
#### Post date: [August 30, 2017, 10:29pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646/4 "2017-08-30T22:29:38Z")
He wants `s` to be an instance of `Real`, not a subtype of `Real`. It’s not currently supported. See e.g. [https://github.com/JuliaLang/julia/issues/9580#issuecomment-101408507](https://github.com/JuliaLang/julia/issues/9580#issuecomment-101408507).
---
### Author:  [@tkoolen](https://discourse.julialang.org/u/tkoolen)
#### Post date: [August 30, 2017, 10:37pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646/5 "2017-08-30T22:37:16Z")
FWIW, I think if this were to be implemented, I think
```julia
struct DiscreteShift{m isa Int} <: AbstractSymmetry end
```
would be more consistent than
```julia
struct DiscreteShift{m::Int} <: AbstractSymmetry end
```
because outside of type definitions `m<:Foo` returns a boolean, whereas `m::Int` is a type assertion, as noted in @yuyichao’s comment, and `m isa Int` would also return a boolean.
---
### Author:  [@gasagna](https://discourse.julialang.org/u/gasagna)
#### Post date: [August 30, 2017, 10:39pm UTC](https://discourse.julialang.org/t/type-of-type-parameters/5646/6 "2017-08-30T22:39:44Z")
> [@tkoolen](#):
>
> struct DiscreteShift{m::Int} \<: AbstractSymmetry end
This syntax would be closer to method definitions, though.