Constructor with a vector of parameters doesn't seem to be recognized?

New to Julia
1

Minimal working example:

struct PureComponentData{Q, T}

    ΔGf::T
    ΔHf::T
    ΔSf::T
    ΔGm::T
    ΔHm::T
    ΔSm::T 
    Tm::T
    Cp::Q
end 

struct CpData{T}
    Tmin::T
    Tmax::T
    a::T
    b::T
    c::T
    d::T
end

function PureComponentData{Q,T}(params::Vector{T}, Cp::Q) where {Q,T}
    if length(params) != 7
        throw(ArgumentError("Must supply the correct number of parameters for Component Data"))
    end
    return PureComponentData(params..., Cp)
end

function __main__()
    Cp = CpData(0,0,0,0,0,0)
    Compound = PureComponentData([1,1,1,1,1,1], Cp)
end

Running this file, I get:

julia> __main__()
ERROR: MethodError: no method matching PureComponentData(::Array{Int64,1}, ::CpData1{Int64})
Closest candidates are:
  PureComponentData(::T, ::T, ::T, ::T, ::T, ::T, ::T, ::Q) where {Q, T} at /path/to/file.jl:3
Stacktrace:
 [1] __main__() at /path/to/file.jl:31
 [2] top-level scope at none:0

Why isn’t Julia recognizing the alternate constructor? What should I do instead?

2

The constructor signature isn’t correct. Try this:

function PureComponentData(params::Vector{T}, Cp::CpData{Q}) where {Q,T}
    if length(params) != 7
        throw(ArgumentError("Must supply the correct number of parameters for Component Data"))
    end
    return PureComponentData(params..., Cp)
end
3 Likes
3

Thanks for your answer! I was hopeful, but the error persists after making that change. Did you test it? Any other ideas?

4

Yes. Perhaps you can restart REPL and try again? Just post your new findings here.

5

I’m still getting the same error. This is the file I’m running now:

struct PureComponentData{Q, T}

    ΔGf::T
    ΔHf::T
    ΔSf::T
    ΔGm::T
    ΔHm::T
    ΔSm::T 
    Tm::T
    Cp::Q
end 

struct CpData{T}
    Tmin::T
    Tmax::T
    a::T
    b::T
    c::T
    d::T
end

function PureComponentData(params::Vector{T}, Cp::CpData{Q}) where {Q,T}
    if length(params) != 7
        throw(ArgumentError("Must supply the correct number of parameters for Component Data"))
    end
    return PureComponentData(params..., Cp)
end
function __main__()
    Cp = CpData(0,0,0,0,0,0)
    Compound = PureComponentData([1,1,1,1,1,1], Cp)
end

And it gives the same error:

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.1.0 (2019-01-21)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                                                                                      `

julia> include("mwe.jl")
__main__ (generic function with 1 method)

julia> __main__()
ERROR: MethodError: no method matching PureComponentData(::Array{Int64,1}, ::CpData1{Int64})
Closest candidates are:
  PureComponentData(::T, ::T, ::T, ::T, ::T, ::T, ::T, ::Q) where {Q, T} at /path/to/mwe.jl:3
Stacktrace:
 [1] __main__() at /path/to/mwe.jl:3:31
 [2] top-level scope at none:0
6

I copied and paste your mwe.jl content and ran it without any problem. However, I’m curious why you have CpData1 instead of CpData in the error message?

7

… Well. D’Oh. I had the name CpData1 in the original code, which helped me figure out the reason the updated version wasn’t working correctly. I hadn’t actually saved the file after changing it. Now it does indeed work great!

8

I have one final question here. So in general then, for some type MyStruct{T, U}:

struct MyStruct{T,U}
    x::T 
    y::U 
end

Is it true that you can’t define some outer constructor
MyStruct{T,U}(x::T, y::U) = MyStruct(x,y) and then call it with some y that is itself a parametric type? If so, why not?

9

No, whether or not y has a parametric type is of no significance. An outer constructor of the form:

Foo{T}(...) where {T} = ...

is only invoked if you actually call it with some {T} at the call site (as in f = Foo{Int}(...) not f = Foo(...)). That’s the only reason your initial code didn’t work. If you want an outer constructor that doesn’t require the {T} to be specified, then you would define it as

Foo(...) where {...} = ...
1 Like
10

Ooooooohhh. Thank you. I read through the docs on constructors and didn’t understand that at all. Perhaps that point should be added to the manual, or clarified.