triangularProbeCountFromIndex

import std.typecons : Nullable;
alias T = Nullable!int;

immutable length = 0;
immutable hitKey = T(42); // key to store
auto haystack = new T[length];

assert(haystack.triangularProbeFromIndex!((T element) => (element is hitKey ||
														  element.isNull))(0) == haystack.length);
assert(haystack.triangularProbeFromIndex!((size_t index, T element) => true)(0) == 0);
assert(haystack.triangularProbeFromIndex!((size_t index, T element) => false)(0) == haystack.length);

import std.typecons : Nullable;
alias T = Nullable!int;

foreach (immutable lengthPower; 0 .. 20) {
	immutable length = 2^^lengthPower;

	immutable hitKey = T(42);  // key to store
	immutable missKey = T(43); // other key not present

	auto haystack = new T[length];
	haystack[] = T(17);	 // make haystack full
	haystack[$/2] = hitKey;

	alias elementHitPredicate = element => (element is hitKey || element.isNull);
	alias elementMissPredicate = element => (element is missKey || element.isNull);

	// key hit
	assert(haystack.triangularProbeFromIndex!(elementHitPredicate)(lengthPower) != haystack.length);

	// key miss
	assert(haystack.triangularProbeFromIndex!(elementMissPredicate)(lengthPower) == haystack.length);
}