On 07/09/2017 11:51 PM, biocyberman wrote:
Following is the code for a more generalized Fibonacci range.
Questions:
1. How do I get only the value of the Nth (i.e. N = 25) element in an
idiomatic way?
As you've only got an input range, you have to popFront the 24 values
that come before. You can use std.range.drop:
----
import std.range : drop;
auto twentyfifth = fib.drop(24).front;
----
But if you're not sure that the range actually has 25 elements, you
should check `empty`, of course:
----
import std.range : popFrontN;
fib.popFrontN(24); /* or fib = fib.drop(24); */
if (!fib.empty)
{
auto twentyfifth = fib.front;
}
----
2. Can I set constraints in the range so that user gets warning if he
asks for Nth element greater than a limit, say N> 30;
You can keep track of N in FibonacciRange and when it hits 30 you throw
an exception or print a message or just set `empty` to true.
You can't make it a compilation warning/error as far as I can tell.
or if the actually
range value at N is greater than datatype limit (e.g. max long)?
You can use std.experimental.checkedint to detect it at run time:
----
private bool _empty = false;
bool empty() const @property { return _empty; }
void popFront()
{
import std.experimental.checkedint : checked, Throw;
long tmp = 0;
try tmp = (checked!Throw(first)*multifactor + second).get;
catch (Throw.CheckFailure e) _empty = true;
first = second;
second = tmp;
}
----
(There may be a smarter way than making the operation throw an exception
and catching that.)
