add ipairs function that respects __index

3 files changed, 38 insertions, 3 deletions

diff --git a/README.md b/README.md
index 7099702..5adaa38 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,7 @@ your project:
   to Lua 5.3's string packing!)
 * `math.maxinteger` and `math.mininteger`, `math.tointeger`, `math.type`,
   and `math.ult`
+* `ipairs` respects `__index` metamethod
 
 ### C
 
@@ -113,7 +114,7 @@ For Lua 5.1 additionally:
 * integer division operator
 * `table.move`
 * `coroutine.isyieldable`
-* `ipairs` and the `table` library don't respect metamethods yet
+* `table` library doesn't respect metamethods yet
 * Lua 5.1: `_ENV`, `goto`, labels, ephemeron tables, etc. See
   [`lua-compat-5.2`][2] for a detailed list.
 * the following C API functions/macros:
diff --git a/compat53.lua b/compat53.lua
index 0346cb7..8bf6bd8 100644
--- a/compat53.lua
+++ b/compat53.lua
@@ -1,6 +1,11 @@
 local lua_version = _VERSION:sub(-3)
 
 if lua_version ~= "5.3" then
+   local _type = type
+   -- select the most powerful getmetatable function available
+   local gmt = _type(debug) == "table" and debug.getmetatable or
+               getmetatable or function() return false end
+   local checkinteger -- forward declararation
 
    -- load utf8 library
    local ok, utf8lib = pcall(require, "compat53.utf8")
@@ -41,7 +46,6 @@ if lua_version ~= "5.3" then
       math.maxinteger = maxint
       math.mininteger = minint
 
-      local _type = type
       function math.tointeger(n)
          if _type(n) == "number" and n <= maxint and n >= minint and n % 1 == 0 then
             return n
@@ -62,7 +66,7 @@ if lua_version ~= "5.3" then
       end
 
       local _error = error
-      local function checkinteger(x, i, f)
+      function checkinteger(x, i, f)
          local t = _type(x)
          if t ~= "number" then
             _error("bad argument #"..i.." to '"..f..
@@ -88,6 +92,26 @@ if lua_version ~= "5.3" then
       end
    end
 
+
+   -- ipairs should respect __index metamethod
+   do
+      local _ipairs = ipairs
+      local function ipairs_iterator(st, var)
+         var = var + 1
+         local val = st[var]
+         if val ~= nil then
+            return var, st[var]
+         end
+      end
+      function ipairs(t)
+         if gmt(t) ~= nil then -- t has metatable
+            return ipairs_iterator, t, 0
+         else
+            return _ipairs(t)
+         end
+      end
+   end
+
 end
 
 -- vi: set expandtab softtabstop=3 shiftwidth=3 :
diff --git a/tests/test.lua b/tests/test.lua
index ac415bc..ab25820 100755
--- a/tests/test.lua
+++ b/tests/test.lua
@@ -22,6 +22,16 @@ end
 print( "testing Lua API ..." )
 package.path = "../?.lua;"..package.path
 require("compat53")
+
+___''
+do
+  local t = setmetatable( {}, { __index = { 1, false, "three" } } )
+  for i,v in ipairs(t) do
+    print("ipairs", i, v)
+  end
+end
+
+
 ___''
 print("math.maxinteger", math.maxinteger+1 > math.maxinteger)
 print("math.mininteger", math.mininteger-1 < math.mininteger)