From 0707e71c6ce9535c08dd3f64897a2987e5706548 Mon Sep 17 00:00:00 2001
From: gamax92 <gamax92@aol.com>
Date: Sun, 11 Aug 2019 12:14:21 +0200
Subject: [PATCH] Support __pairs and __ipairs

Added PAIRS and IPAIRS constants to LuaValue
Merged pairs and ipairs into one class with a dynamic constructor, this
is similar to Lua's pairsmeta function.
Check for and call it's specific metamethod if it's available.
---
 src/core/org/luaj/vm2/LuaValue.java    | 10 +++++--
 src/core/org/luaj/vm2/lib/BaseLib.java | 37 ++++++++++++++------------
 2 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/src/core/org/luaj/vm2/LuaValue.java b/src/core/org/luaj/vm2/LuaValue.java
index af249516..349044e6 100644
--- a/src/core/org/luaj/vm2/LuaValue.java
+++ b/src/core/org/luaj/vm2/LuaValue.java
@@ -99,7 +99,7 @@ package org.luaj.vm2;
  * {@link #INDEX}, {@link #NEWINDEX}, {@link #CALL}, {@link #MODE}, {@link #METATABLE},
  * {@link #ADD}, {@link #SUB}, {@link #DIV}, {@link #MUL}, {@link #POW},
  * {@link #MOD}, {@link #UNM}, {@link #LEN}, {@link #EQ}, {@link #LT},
- * {@link #LE}, {@link #TOSTRING}, and {@link #CONCAT}.
+ * {@link #LE}, {@link #TOSTRING}, {@link #CONCAT}, {@link PAIRS} and {@link IPAIRS}.
  * 
  * @see org.luaj.vm2.lib.jse.JsePlatform
  * @see org.luaj.vm2.lib.jme.JmePlatform
@@ -242,7 +242,13 @@ public class LuaValue extends Varargs {
 
 	/** LuaString constant with value "__concat" for use as metatag */
 	public static final LuaString CONCAT      = valueOf("__concat");
-	
+
+	/** LuaString constant with value "__pairs" for use as metatag */
+	public static final LuaString PAIRS = valueOf("__pairs");
+
+	/** LuaString constant with value "__ipairs" for use as metatag */
+	public static final LuaString IPAIRS = valueOf("__ipairs");
+
 	/** LuaString constant with value "" */
 	public static final LuaString EMPTYSTRING = valueOf("");
 
diff --git a/src/core/org/luaj/vm2/lib/BaseLib.java b/src/core/org/luaj/vm2/lib/BaseLib.java
index d0dbf6b3..cea359b6 100644
--- a/src/core/org/luaj/vm2/lib/BaseLib.java
+++ b/src/core/org/luaj/vm2/lib/BaseLib.java
@@ -113,8 +113,8 @@ public class BaseLib extends TwoArgFunction implements ResourceFinder {
 
 		next next;
 		env.set("next", next = new next());
-		env.set("pairs", new pairs(next));
-		env.set("ipairs", new ipairs());
+		env.set("pairs", new pairsbase(PAIRS, NIL, next));
+		env.set("ipairs", new pairsbase(IPAIRS, ZERO, new inext()));
 		
 		return env;
 	}
@@ -395,23 +395,26 @@ public class BaseLib extends TwoArgFunction implements ResourceFinder {
 			}
 		}
 	}
-	
-	// "pairs" (t) -> iter-func, t, nil
-	static final class pairs extends VarArgFunction {
-		final next next;
-		pairs(next next) {
-			this.next = next;
+
+	// pairsbase, // (t) -> iter-func, t, initial
+	static final class pairsbase extends VarArgFunction {
+		final LuaString method;
+		final LuaValue initial;
+		final VarArgFunction iter;
+
+		pairsbase(LuaString method, LuaValue initial, VarArgFunction iter) {
+			this.method = method;
+			this.initial = initial;
+			this.iter = iter;
 		}
+
 		public Varargs invoke(Varargs args) {
-				return varargsOf( next, args.checktable(1), NIL );
-		}
-	}
-	
-	// // "ipairs", // (t) -> iter-func, t, 0
-	static final class ipairs extends VarArgFunction {
-		inext inext = new inext();
-		public Varargs invoke(Varargs args) {
-			return varargsOf( inext, args.checktable(1), ZERO );
+			LuaValue arg = args.arg1();
+			LuaValue t = arg.metatag(method);
+			if (!t.isnil())
+				// TODO: This can return more than 3 results.
+				return t.invoke(args.isvalue(1) ? arg : t);
+			return varargsOf(iter, args.checktable(1), initial);
 		}
 	}