On Monday, 4 April 2016 at 08:10:10 UTC, Edwin van Leeuwen wrote:
Is there a way to make sure a delegate only reads state,
without changing it? I tried annotating the delegate as const,
but that does not seem to work.
Note that annotating with pure also doesn't help. As a result we
can have a pure delegate that returns different results every
time it is called.
```D
void main()
{
import std.stdio : writeln;
auto r = [0,1,2,3];
auto f = delegate() const pure
{
import std.array : front, popFront;
r.popFront;
return r.front;
};
r.writeln; // [0,1,2,3]
auto f1 = f();
r.writeln; // [1,2,3]
assert( f() == f1 ); // Throws
}
```
