[julia-users] Help with metaprogramming

[Greg Plowman]

Hi
 
I'm trying to automate some code and thought Julia's metaprogramming might 
help, but I've got myself very confused.
 
I have a user-defined composite type, which for different applications, I 
change the fields.
I also want to define some functions for this user type (+, copy, == etc)
because I change the composite fields regularly, I thought I could 
somehow use Julia's introspection / metaprogramming to define these 
functions.
 
Suppose I define:
 

type Counters
    counter1::Array{Int64,1}
    counter2::Array{Int64,1}
    counter3::Array{Int64,1}
    counter4::Array{Int64,1}
    counter5::Array{Int64,2}
 
    # no-argument constructor
    function Counters()
        this = new()
        this.counter1 = zeros(Int64, 100000)
        this.counter2 = zeros(Int64, 100000)
        this.counter3 = zeros(Int64, 100000)
        this.counter4 = zeros(Int64, 500)
        this.counter5 = zeros(Int64, 500, 1000)
        return this
    end
end

 
 
Defined explicitly, my + function would look something like:  
 

function +(c1::Counters, c2::Counters)
    c = Counters()
    c.counter1 = c1.counter1 + c2.counter1
    c.counter2 = c1.counter2 + c2.counter2
    c.counter3 = c1.counter3 + c2.counter3
    c.counter4 = c1.counter4 + c2.counter4
    c.counter5 = c1.counter5 + c2.counter5
    return c
end

 
 
I was hoping I could define implicitly using macros / metaprogramming:
 

function +(c1::Counters, c2::Counters)
    c = Counters()
    
    for field in names(Counters)
        ex = :(c.$field = c1.$field + c2.$field)
        eval(ex)
    end
    
    return c
end

 
I know this doesn't work, but I've tried many variations but always seem to 
get stuck.
I would like the function to be eval-ed and unrolled at compile time, so 
that it executes fast at run time.
 
Can someone point me in the right direction?
 
Thanks, Greg