Julia, MethodError: no method matching

Question

I wanted to test how abstract type works in "strcutres", so I created a struct below with a constructor, however, the return message displays "ERROR: MethodError: no method matching Rect(::Int64)".

I don't know which part went wrong, although the parameter "5" that I used fits the definition of the constuctor which is a single integer input. Thank you.

abstract type Shape{T<:Integer,F<:AbstractFloat} end
export Shape

struct Rect{T,F} <: Shape{T,F}
    a::T
    b::T
    c::T
    v::F
    function Rect{T,F}(a::T) where {T<:Integer, F<:AbstractFloat}
        b = 10;
        c = 10;
        v = a*b*c;
        return new(a,b,c,v)
    end
end

function main()

    vol = Rect(5).v;

    println(vol)

end

main()

It should return a product of a, b and c with only a being the input variable.

Answer 1

You do not have the appropriate constructor. You should do:

julia> Rect{Int,Float64}(5)
Rect{Int64, Float64}(5, 10, 10, 500.0)

Other option is to add the constructor to your struct:

function Rect{T}(a::T) where {T<:Integer}
    Rect{Int,Float64}(a)
end

Once you add the constructor you can do:

julia> Rect{Int}(5)
Rect{Int64, Float64}(5, 10, 10, 500.0)

Or you can also define:

Rect(a::Int) =  Rect{Int,Float64}(a)

and have

julia> Rect(5)
Rect{Int64, Float64}(5, 10, 10, 500.0)