[julia-users] Bug or feature? How does = decide whether to do a copy or deepcopy?

[Eric Ford]

I don't understand why the first function doesn't change x, but the second 
function does.  
Is the = calling deepcopy in f1, but copy in f2?  
If so, why?

function f1(x::Array)
 w = x  
 for i in 1:length(x)
   w[i] += 10.0
 end
 w += 10.0
 return w
end

function f2(x::Array)
 w = x  
 for i in 1:length(x)
   w[i] += 10.0
 end
 w += 10.0
 return w
end

x=randn(10)
x_orig = deepcopy(x)
f_of_x = f(x)
sum((x.-x_orig).^2)

After f1: 0.0
After f2: 1000.0

Thanks,
Eric (on behalf of an Astro 585 student)