On Tuesday, 21 October 2014 at 08:48:09 UTC, safety0ff wrote:
On Tuesday, 21 October 2014 at 08:25:07 UTC, bearophile wrote:
Minas Mina:
Aren't pure functions supposed to return the same result
every time? If yes, it is correct to not accept it.
But how can main() not be pure? Or, how can't the 'a' array be
immutable?
Bye,
bearophile
There can exist a mutable reference to a's underlying memory:
const int[] a;
int[] b;
static this()
{
b = [1];
a = b;
}
`a` isn't a reference to `b`. `a` is assigned by value and has
its own storage. You could change its type to const int[]* a =
&b; then it would be a reference to mutable storage. I made an
example program to figure these things out, or else I wouldn't
know what I'm talking about.
import std.stdio;
import std.conv;
const int[] a;
int[] b;
static this()
{
string entry;
while(entry == "") {
try {
write("enter an int: ");
entry = readln();
b = [to!int(entry[0..entry.length-1])];
} catch(ConvException e) {
writeln("error, try again");
entry = "";
}
}
a = b;
}
int[] x = [0,1,2,3];
class Holder
{
const(int[]) y;
this() { y = x; }
}
void main()
{
auto H = new Holder();
writeln("original const a ", a); // [the int that was entered]
b = [8,7];
writeln("unaltered const a ", a); // [the int that was
entered]
x = [10,9];
writeln("unaltered const member y ", H.y); // [0, 1, 2, 3]
H = new Holder();
writeln("new const member y ", H.y); // [10, 9]
writeln("immutable m ", get_m()); // [42]
}
immutable int[] m = [42];
immutable(int[]) get_m() pure
{
return m;
}
