On Tue, 2014-11-18 at 22:06, David Smith <[email protected]> wrote:
> I would like to have a type such as this:
> type foo{T,M,N}
> x::Array{T,M}
> y::Array{T,N}
> end
>
> Where T and M can be anything, but N = M + 1. I know I can't write
>
> type foo{T,M}
> x::Array{T,M}
> y::Array{T,M+1}
> end
>
> So I wrote the following naive code, but I get an error:
>
> julia> function foo{T,M,N}(x::Array{T,M}, y::Array{T,N})
> @assert (M + 1) == N
> return foo(x,y)
> end
> foo{T,M,N} (constructor with 1 method)
>
> julia> foo(rand(3),rand(3,3))
> ERROR: stack overflow
> in foo at none:2
> in foo at none:3 (repeats 79999 times)
This stackoverflow happens because you call foo again and again...
Anyway, this seems to work:
immutable Foo{T,M,N} # probably want an immutable here, so nobody swaps
# out the arrays behind your back.
x::Array{T,M}
y::Array{T,N}
function Foo(x,y)
@assert (M + 1) == N
new(x,y)
end
end
Foo{T, M, N}(x::Array{T,M}, y::Array{T,N}) = Foo{T, M, N}(x,y)
Foo(rand(3),rand(3,2))
Foo(rand(3),rand(3,2,3)) # errors
Note that the outer constructor is needed, see
http://docs.julialang.org/en/latest/manual/constructors/#parametric-constructors
(Note, types are by convention capitalized)
