Prepending a type to an array

General Usage
1

In reading about mixture models in Distributions.jl, I found this code snippet:
Normal[ Normal(-2.0, 1.2), Normal(0.0, 1.0), Normal(3.0, 2.5)]
This syntax is unfamiliar to me. The only documentation I can find is a brief mention in the Julia manual page for arrays about prepending a type to an array.

What does the Normal in front of the array in the above snippet do, in detail? Is there documentation somewhere?

2

Probably nothing in this case since the elements are already of type Normal.

julia> a = [Float32(1), Float32(2), Float32(3)]
3-element Vector{Float32}:
 1.0
 2.0
 3.0

julia> b = Float32[1, 2, 3]
3-element Vector{Float32}:
 1.0
 2.0
 3.0

julia> eltype(a)
Float32

julia> eltype(b)
Float32

A type declaration in front of the array limits what types can be stored in the array (usually for performance or error checking).

julia> c = [1, "Hello", 3]
3-element Vector{Any}:
 1
  "Hello"
 3

julia> d = Float32[1, "Hello", 3]
ERROR: MethodError: Cannot `convert` an object of type String to an object of type Float32

julia> eltype(c)
Any
1 Like
3

Here’s the relevant documentation: Multi-dimensional Arrays · The Julia Language

2 Likes