Question

Lets say I have an array X that contains [A,B,C,D,nil];

and I have a second array Y that contains [E,F,G,H,I,J,nil];

If I execute the following:

//Append y to x
[x addObjectsFromArray:y];

//Empty y and copy x
[y removeAllObjects];
y = [x mutableCopy];

What is the value of y? is it?:

[A,B,C,D,E,F,G,H,I,J,nil]

Am I performing the copy correctly?

At the end of the operation I want y to be [A,B,C,D,E,F,G,H,I,J]

Answer 1

At the start:

x is [A, B, C, D] (the nil is not part of the array, it just tells initWithObjects: where the end of the list of objects is).
y is [E, F, G, H, I, J]

[x addObjectsFromArray:y]; // only works if x is a mutable array

x is [A, B, C, D, E, F, G, H, I, J]

y is [E, F, G, H, I, J]

[y removeAllObjects]; // only works if y is a mutable array.

x is [A, B, C, D, E, F, G, H, I, J]

y is []

y = [x mutableCopy];

x is [A, B, C, D, E, F, G, H, I, J]

y is [A, B, C, D, E, F, G, H, I, J]

Note that the previous version of y that you emptied may have leaked because you overwrote the pointer with a pointer to a new mutable copy of x. You should have done:

[y release];
y = [x mutableCopy];

Or if you obtained y by using +arrayWithObjects: instead of +alloc followed by -initWithObjects: simply

y = [x mutableCopy]; // release not necessary because you didn't own y (you do now though).