How does Julia pass arguments in functions()
In Julia, the parameter passing mechanism is somewhat nuanced. It commonly follows the "pass-by-sharing" model, which means that:
Immutable objects (e.g., integers, floats, strings) are effectively passed by value because their state cannot be altered. Any change to a function argument inside the function will not affect the original variable.
Mutable objects (e.g., arrays, dictionaries) are passed by reference, and changes to these objects within the function will affect the original object outside the function.
Hence, for mutable objects, sharing is enabled with the caller.
Here's an illustration:
# Immutable example
x = 10
function foo(y)
y = y + 5
end
foo(x)
println(x) # Output: 10
# Mutable example
arr = [1, 2, 3]
function bar(lst)
append!(lst, 4)
end
bar(arr)
println(arr) # Output: [1, 2, 3, 4]In the foo example, the integer x remains unchanged because integers (immutable) are passed by value-like semantics. In the bar example, the array arr is modified because arrays (mutable) are passed by reference-like semantics.
Creating Static Copies
If you want to ensure that a function works with a copy of an object (thus simulating "pass-by-value" for mutable objects), you can create a copy of the object when passing it to the function. Use functions like copy() or deepcopy() in Julia to achieve this:
copy()performs a shallow copy.deepcopy()performs a deep copy.
Here's an example:
arr = [1, 2, 3]
function qux(lst)
lst_copy = copy(lst)
append!(lst_copy, 4)
return lst_copy
end
new_arr = qux(arr)
println(arr) # Output: [1, 2, 3] (original array remains unchanged)
println(new_arr) # Output: [1, 2, 3, 4] (copied and modified array)In this code, qux makes a shallow copy of arr and modifies the copy, leaving the original array unchanged.
Relevant Resources
By understanding the difference and the behavior of mutable and immutable objects in Julia, you can effectively control whether a function argument should reflect changes outside the function or not.
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