How to hijack UnionAll type creation process?

General Usage
1

Hi,

is it possible to do such a thing?

struct MM{T}
  x::T
end
#when I do this
MM{Int}
#I want it to return
MM{Float64}

I tried the following but didn’t work:

function (::Base.Type{Type{MM}})(::Type{Int})
           MM{Float64}
       end
2

No. Why?

3

like that ?

struct MM{T}
  x::T
end

MM(x::Int) = MM(float(x))

julia> MM(1)
MM{Float64}(1.0)