Declare the size of an array attribute in a type definition

Question

I currently have a type with an array attribute

immutable foo a::Int64 b::Int64 x::Array{Float64,1} # One dimension array of Float 64, but no length info end 

I know that an array will always contain 100 Float64 elements. Is there a way to pass this information into type annotations? Perhaps something similar to how you can declare the size of an array instance like x = Array(Float64, 100) ?

Answer 1

You can force invariants with an internal constructor.

 immutable Foo a::Int64 b::Int64 x::Vector{Float64} # Vector is an alias for one-dimensional array function Foo(a,b,x) size(x,1) != 100 ? error("vector must have exactly 100 values") : new(a,b,x) end end 

And then from REPL:

 julia> Foo(1,2,float([1:99])) ERROR: vector must have exactly 100 values in Foo at none:7 julia> Foo(1,2,float([1:100])) Foo(1,2,[1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0 … 91.0,92.0,93.0,94.0,95.0,96.0,97.0,98.0,99.0,100.0])