On Thursday, 5 August 2021 at 01:14:26 UTC, H. S. Teoh wrote:
On Thu, Aug 05, 2021 at 12:47:06AM +0000, someone via
Digitalmars-d-learn wrote:
[...]
1) If the constant is a POD (int, float, etc.), use:
enum myValue = ...;
2) If the constant is a string or some other array:
static immutable string myString = "...";
static immutable Data[] myData = [ ... ];
Unless you have a specific reason to, avoid using `enum` with
string and array literals, because they will trigger a memory
allocation *at every single reference to them*, which is
probably not what you want.
enum myArray = [ 1, 2, 3 ];
...
int[] data = myArray; // allocates a new array
int[] data2 = myArray; // allocates another array
// they are separate arrays with the same contents
assert(data !is data2);
assert(data == data2);
// allocates a temporary array, does the comparison, then
// discards the temporary
if (data == myArray) ...
foreach (i; 0 .. 10) {
int[] input = getUserInput(...);
// allocates a new array at every single loop iteration
if (input == myArray) { ... }
}
Don't do this. Use static immutable for arrays and strings, use
enum only for PODs.
T
The fact it requires this much explanation on how to declare a
"best/proper" constant is not a great selling point for D. Sure,
it is easy...once you know it and it reminds me of C++.
As a language D should strive to do better than this
