🚴 perf(concat): Exploit implicit prototype branching.

Author: make-github-pseudonymous-again

src/0-core/_fast/_app3.js

@@ -0,0 +1,18 @@
+import assert from 'assert';
+
+export default function _append_small_list(tree, list) {
+	assert(Number.isInteger(list.length) && list.length >= 0 && list.length <= 4);
+	// eslint-disable-next-line default-case
+	switch (list.length) {
+		case 0:
+			return tree;
+		case 1:
+			return tree.push(list[0]);
+		case 2:
+			return tree.push(list[0]).push(list[1]);
+		case 3:
+			return tree.push(list[0]).push(list[1]).push(list[2]);
+		case 4:
+			return tree.push(list[0]).push(list[1]).push(list[2]).push(list[3]);
+	}
+}