Sync

Task/Generator-Exponential/D/generator-exponential-3.d

@@ -0,0 +1,47 @@
+import std.stdio, std.bigint, std.range, std.algorithm;
+
+struct Filtered(R1, R2) if (is(ElementType!R1 == ElementType!R2)) {
+    R1 s1;
+    R2 s2;
+    alias ElementType!R1 T;
+    T front, source, filter;
+
+    this(R1 r1, R2 r2) {
+        s1 = r1;
+        s2 = r2;
+        source = s1.front;
+        filter = s2.front;
+        popFront;
+    }
+
+    static immutable empty = false;
+
+    void popFront() {
+        while (true) {
+            if (source > filter) {
+                s2.popFront;
+                filter = s2.front;
+                continue;
+            } else if (source < filter) {
+                front = source;
+                s1.popFront;
+                source = s1.front;
+                break;
+            }
+            s1.popFront;
+            source = s1.front;
+        }
+    }
+}
+
+auto filtered(R1, R2)(R1 r1, R2 r2) // Helper function.
+if (isInputRange!R1 && isInputRange!R2 &&
+    is(ElementType!R1 == ElementType!R2)) {
+    return Filtered!(R1, R2)(r1, r2);
+}
+
+void main() {
+    auto squares = 0.sequence!"n".map!(i => i.BigInt ^^ 2);
+    auto cubes = 0.sequence!"n".map!(i => i.BigInt ^^ 3);
+    filtered(squares, cubes).drop(20).take(10).writeln;
+}