[julia-users] Re: Managing objects and state

[James Fairbanks]

If you want to use julia functions like OOP methods just make the first 
argument the object instance so

function setx!(s::State, i::int)
#modifies s, so we use "!" in function name 
s.x = i
end

function squarex(s::State)
   return s.x^2
end

#main code
s = State()
setx!(s,2)
#s.x == 2
y =squarex(s)
#y == 4

If you adopt the convention that the "object" is the first argument to the 
function and the later arguments are the parameters of the method, 
s.method(param) translates to function(s, param). So your zero argument 
functions that modify program state become one argument functions that 
modify the state variable that is passed to them. Keep in mind the well 
loved Julia convention that functions which modify their arguments should 
end in "!" like "setx!(s::State)" or "increment!(c::Counter)".

Does this make things easier to reason about? 

James

[julia-users] Re: Managing objects and state

[Bob Cowdery]

Thanks. So the type instance is passed in as a parameter. My problem is 
that if this is a remote call I can't see how to handle the state without 
having a global instance of State. Something like this so I first remote 
call somefunction() which sets some state and then remote call 
anotherfunction() which adds the parameter before it calls the 
realanotherfunction(). Having been warned away from using globals this 
seems a bad solution. Is there another way to do this?

type State
  x::int
end

s = State

function somefunction()
  ...
  s.x = 1
  ...
end

function anotherfunction()
  realanother(s)
end

realanotherfunction(s::State)
  ...
  s.x = 10
  ...
end





On Monday, March 24, 2014 7:32:41 PM UTC, Bob Cowdery wrote:
>
> Forgive me if this is daft and often answered question but I'm trying to 
> get my head around Julia OO.
>
> Am I correct in thinking that as there is no binding between methods and 
> types that I have to explicitly pass in an instance of a type to a method.
> If that is the case then how do I hold state on a remote object. I call a 
> function that creates an instance of a type say something simple.
> type State 
>
>   sock
>
> end
> I just want to hold a socket reference. If the first remote function I call 
> creates State then how can the next function I call obtain the state instance.
>
> Do I have to create a remote reference or something which it can use?
>
> Thanks
> Bob
>
>
>

[julia-users] Re: Managing objects and state

[andrew cooke]

it's not completely clear to me what you're asking.  julia isn't 
particularly object oriented (i just checked and there's no mention of 
objects or classes in the intro at http://julialang.org/)

having said that, you can store and modify (unless the type is immutable) 
values in composite types.  so, for example


julia> type State
   x::Int
   end

julia> function set(s::State, x::Int)
   s.x = x
   end
set (generic function with 1 method)

julia> function read(s::State)
   return s.x
   end
read (generic function with 1 method)

julia> s = State(12)
State(12)

julia> s.x
12

julia> s.x = 100
100

julia> s.x
100

julia> s
State(100)

julia> set(s, 32)
32 
 


julia> s   
 
State(32)   



julia> read(s)
32

maybe that helps?  obviously set and read are trivial to do directly on the 
instance, but you could imagine more complex functions.

andrew

  
On Monday, 24 March 2014 16:32:41 UTC-3, Bob Cowdery wrote:
>
> Forgive me if this is daft and often answered question but I'm trying to 
> get my head around Julia OO.
>
> Am I correct in thinking that as there is no binding between methods and 
> types that I have to explicitly pass in an instance of a type to a method.
> If that is the case then how do I hold state on a remote object. I call a 
> function that creates an instance of a type say something simple.
> type State 
>
>   sock
>
> end
> I just want to hold a socket reference. If the first remote function I call 
> creates State then how can the next function I call obtain the state instance.
>
> Do I have to create a remote reference or something which it can use?
>
> Thanks
> Bob
>
>
>