Julia equivalent to a static member function in C++/MATLAB

[Joel Andersson]

Hi,

In C++ or in MATLAB I would use static member functions to keep the constructors nice and simple, e.g.

class MyMatrix {
  public:
  static MyMatrix zeros(int n, int m);
  static MyMatrix ones(int n, int m);
  static MyMatrix eye(int n);
  ...
};

Which allows me to create class instances with an IMO natural syntax, which should also be relatively efficient due to return value optimization:

MyMatrix x = MyMatrix::zeros(3,4);

In MATLAB, I would do the same with a static method, e.g.:

x = MyMatrix.zeros(3,4);

What is the equivalent way to do it in Julia? I have seen discussions of whether and how to overload the dot operator ".", but I did not fully understand if this discussion applies to the above case or if that's already possible somehow.

Best regards,

Joel

[Steven G. Johnson]

On Friday, September 25, 2015 at 11:56:46 AM UTC-4, Joel Andersson wrote:

Hi,

In C++ or in MATLAB I would use static member functions to keep the constructors nice and simple, e.g.

class MyMatrix {
  public:
  static MyMatrix zeros(int n, int m);
  static MyMatrix ones(int n, int m);
  static MyMatrix eye(int n);
  ...
};

Which allows me to create class instances with an IMO natural syntax, which should also be relatively efficient due to return value optimization:

MyMatrix x = MyMatrix::zeros(3,4);

In Julia, you can do the same thing, it is just spelled differently.  You could do

     x = zeros(MyMatrix, 3, 4)

where you have defined

     Base.zeros(::Type{MyMatrix}, m, n) = .....

[Joel Andersson]

Great, thanks! Joel

[Greg Plowman]

 

In Julia, you can do the same thing, it is just spelled differently.  You could do 

   x = zeros(MyMatrix, 3, 4)

where you have defined

     Base.zeros(::Type{MyMatrix}, m, n) = .....

Show trimmed content

Of course in Julia you can do anything you want.

However, is it recommended to redefine the meaning of generic functions?

I would assume zeros(MyMatrix,3,4) creates a 3x4 Array{MyMatrix,2}

[Eric Forgy]

You probably know this, but the way dispatch works in Julia, it will look for a function matching the signatures. Since, presumably, MyMatrix is not in base Julia, that zeros function will do whatever you want it to do because you have yo implement it.

[Joel Andersson]

Yes, this is all clear. Joel