On Monday, 3 December 2018 at 20:37:22 UTC, Jonathan M Davis
wrote:
On Monday, December 3, 2018 1:07:24 PM MST Goksan via
Digitalmars-d-learn wrote:
Are there any differences between these 2 methods of copying
elements?
double[] array = [ 1, 20, 2, 30, 7, 11 ];
// Non dup
double[6] bracket_syntax_dup = array;
bracket_syntax_dup[] = array;
bracket_syntax_dup[0] = 50;
// Dup
double[6] normal_dup = array.dup;
normal_dup[0] = 100;
OUTPUT: (array, bracket_syntax_dup and normal_dup
respectively):
[1, 20, 2, 30, 7, 11]
[50, 20, 2, 30, 7, 11]
[100, 20, 2, 30, 7, 11]
dup allocates a new dynamic array and copies the elements of
the existing dynamic array to the new one. Calling dup in order
to assign to a static array is just needlessly allocating a
dynamic array. The contents of the array are going to be copied
to the static array regardless, but instead of just copying the
elements, if you use dup, you're allocating a new dynamic
array, copying the elements into that dynamic array, and then
you're copying the elements into the static array. There's no
point.
You use dup when you want to copy the elements of a dynamic
array instead of simply slicing it. Slicing gives you a new
dynamic array that points to exactly the same elements. It's
just copying the pointer and the length (meaning that mutating
the elements of the new slice will affect the elements in the
original array), whereas dup actually allocates a new block of
memory for the new dynamic array to be a slice of (copying the
elements over in the process), so mutating the elements in the
new dynamic array then won't affect the elements in the
original.
Regardless, when you create a static array, it's not a slice of
anything (since its elements sit directly on the stack), and
when assign to it, you're simply copying the elements over.
- Jonathan M Davis
Then shouldn't the following output false, false, true?
import std.stdio;
class Programmer
{
bool is_confused = false;
void setConfusion(bool confusion_status)
{
is_confused = confusion_status;
}
}
void main()
{
Programmer[6] array = new Programmer();
Programmer[6] bracket_syntax_dup = array;
bracket_syntax_dup[] = array;
Programmer[6] normal_dup = array.dup;
normal_dup[0].setConfusion(true);
bracket_syntax_dup[0] = new Programmer();
writeln(array[0].is_confused);
writeln(bracket_syntax_dup[0].is_confused);
writeln(normal_dup[0].is_confused);
}
