How does Julia invoke constructors with overlapping constraints

New to Julia
1

Hello, I am playing with constructors, but seems, that Julia allows to have constructor with overlapping constrains N.

using StaticArrays: SizedVector

mutable struct Context{TYPE_VAR_STACK <: Union{UInt8, UInt16}, N <:Union{UInt8, UInt16}}
    stack::SizedVector
    index::N 

    # Constructor constraint for N <:UInt8
    function Context(stack_type::Type{T}, stack_length::N, def_stack_val=eltype(stack_type)(0),) where {T <: Union{UInt8, UInt16}, N <: Union{UInt8}}
        
        println("ctor UInt8")
        # StaticArrays pkg doesn't allow to have its Size in different types than Int
        size = Int(stack_length)
        new{T, N}(SizedVector{size}(fill(def_stack_val, size)), size)
        
    end

    # More general constructor for N <:Union{UInt8 and UInt16}
    function Context(stack_type::Type{T}, stack_length::N, def_stack_val=eltype(stack_type)(0),) where {T <: Union{UInt8, UInt16}, N <: Union{UInt8, UInt16}}
        # StaticArrays pkg doesn't allow to have its Size in different types than Int
        size = Int(stack_length)
        new{T, N}(SizedVector{size}(fill(def_stack_val, size)), size)
        
    end


end


# More specific
julia> Context(UInt16, UInt8(100))
ctor UInt8
Context{UInt16, UInt8}(UInt16[0, 0, 0, 0, 0, 0, 0, 0, 0, 0  …  0, 0, 0, 0, 0, 0, 0, 0, 0, 0], 100)
# More specific
julia> Context(UInt8, UInt8(100))
ctor UInt8
Context{UInt8, UInt8}(UInt8[0, 0, 0, 0, 0, 0, 0, 0, 0, 0  …  0, 0, 0, 0, 0, 0, 0, 0, 0, 0], 100)

# More generic
julia> Context(UInt8, UInt16(100))
Context{UInt8, UInt16}(UInt8[0, 0, 0, 0, 0, 0, 0, 0, 0, 0  …  0, 0, 0, 0, 0, 0, 0, 0, 0, 0], 100)

and methods

julia> methods(Context)
# 4 methods for type constructor:
 [1] Context(stack_type::Type{T}, stack_length::N) where {T<:Union{UInt16, UInt8}, N<:UInt8}
     @ ~/devel/julia/bf/bf.jl:8
 [2] Context(stack_type::Type{T}, stack_length::N, def_stack_val) where {T<:Union{UInt16, UInt8}, N<:UInt8}
     @ ~/devel/julia/bf/bf.jl:8
 [3] Context(stack_type::Type{T}, stack_length::N, def_stack_val) where {T<:Union{UInt16, UInt8}, N<:Union{UInt16, UInt8}}
     @ ~/devel/julia/bf/bf.jl:18
 [4] Context(stack_type::Type{T}, stack_length::N) where {T<:Union{UInt16, UInt8}, N<:Union{UInt16, UInt8}}
     @ ~/devel/julia/bf/bf.jl:18

I have several question:

  1. Is there some kind of internal mechanism, that uses more specific constructor?
  2. Is there possibility to call more general constructor?
2
  1. The same way as for any other function multiple dispatch/method specificity Methods · The Julia Language
  2. invoke