Hello, everyone, This is rudimentary, but I’am confused about Julia’s different “=” behaviors for Numbers and Arrays. To my understanding, when we assign a variable to an object, we set the variable referred to the memory location of the object. Then if we assign this variable to another variable, behavior changes between numbers and arrays. Like this: julia> x = 10 10 julia> x1 = x 10 julia> x1 === x true julia> x1 = 5 5 julia> x 10 julia> x1 === x false Which means for numbers, x1 initially is exactly the same with x before we assign a new object to it. But for Arrays, this is a different story, like this: julia> y = [10] 1-element Array{Int64,1}: 10 julia> y1 = y 1-element Array{Int64,1}: 10 julia> y1 === y true julia> y1[1] = 3 3 julia> y 1-element Array{Int64,1}: 3 julia> y1 === y true Which means y1 and y always point to the same memory location. But we can use copy() and deepcopy() to separate y1 and y. I know this is rudimentary, but I’m really curious about why it is designed this way? Why don’t we align these two different behaviours? Can anyone explain to me the mechanism underground? Thanks!

This is a common source of confusion for beginners (myself included). You can find related threads about it. One nice answer is this one: [image] Assignment and mutation New to Julia The simplest version of this I can come up with is this: Assignment changes which object a name refers to: x = ex causes the name x to refer to the value resulting from the evaluation of the expression ex. Assignment never changes the values of any objects. Mutation changes the value of an object: x[i] = ex and x.f = ex both mutate the object referred to by x changing a value at index or a property with a name, respectively. Mutation never changes what objects any names in any scope refer …

thank you for the link, very clearly explained!

Confused by different behavior of assignments of Arrays and Numbers

New to Julia

lmiq November 15, 2020, 12:48pm 2

This is a common source of confusion for beginners (myself included). You can find related threads about it. One nice answer is this one:

Topic		Replies	Views
Assignment and mutation New to Julia question	6	7217	December 31, 2018
What is the philosophy behind arrays not being copied when assigned to another variable? New to Julia	24	3033	May 19, 2023
Array assignment is alias and assignment semantics New to Julia array	7	1114	April 7, 2021
Assignment of array elements New to Julia question	2	5408	February 1, 2018
When will the original value be changed with the copied value? New to Julia question	8	1775	April 21, 2020

Confused by different behavior of assignments of Arrays and Numbers

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