Create README.md

README.md

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+# Lua
+
+This repo is a clone of the official Lua repository https://github.com/lua/lua, where I publish my own changes and improvements.
+
+This branch implements…
+
+## Direct enumeration of collections in Lua `for in` loops.
+
+This branch adds support for direct `for..in` enumeration in Lua, for any type of collection: Lua tables and native collections 
+implemented as userdata, without having to call `pair()` or `ipair()`, in the for-in statement.
+
+For example, you can now write:
+
+````Lua
+for var1, var2, var3 in collection do
+    -- do some stuff
+end
+````
+
+Direct `for..in` enumeration can be customized by defining a `"__forgen"` metamethod that shall return the 3 values needed 
+by the generic for loop: an iterator function, a state, and the initial value of the iterator variable.  
+
+If no `"__forgen"` metamethod is defined and the collection is a Lua table, direct for..in enumeration is equivalent to 
+calling the standard Lua library function `pair()`.
+
+Internally, a new Lua op-code 'OP_TFORPREP' has been added, that replaces the initial JMP instruction when initializing 
+a generic for loop. When executed, this opcode checks for the presence of a "__forgen" metamethod in the loop base object 
+and calls it if present.