Differences between WattleScript Lua and Lua

WattleScript’s Lua mode contains minor differences and a few additions, inherited from MoonSharp.

List of Differences

• Strings are Unicode: some caution is required if code uses strings to store binary data. On the other hand, strings used as real strings are a lot easier to use.
• Garbage Collection is different, as WattleScript makes use of the .NET GC. Notably this makes collectgarbage() a no-op.
• Compatibility is source-only, WattleScript cannot load luac binaries.
• Slight differences in error messages.
• Function names are tracked at function declaration, not backtracked at function calls like in Lua (noticeable only when debugging)

List of Additions

• Multiple expressions can be used as indices but the value to be indexed must be a userdata, or a table resolving to userdata through the metatable (but without using metamethods). So, for example, x[1,2,i] is parsed correctly but might raise an error if x is not a userdata.
• Metalua short anonymous functions (lambda-style) are supported. So |x, y| x + y is shorthand for function(x,y) return x+y end.
• A non-yieldable __iterator metamethod has been added. It’s called if the argument f of a for ... in ... loop is not actually a function.
• A default iterator is provided if the argument f of a for ... in ... loop is a table without __iterator or __call metamethods. The provided result is value, key unlike ipairs or pairs.
• \u{xxx} escapes, where x are up to 8 hexadecimal digits, are supported inside strings and will output the specified Unicode codepoint, as it does in Lua 5.3
• loadsafe and loadfilesafe methods, same as load and loadfile but defaulting to the current top-of-the-stack _ENV instead of the default one, for easier sandboxing
• The dynamic.eval and dynamic.prepare functions to handle dynamic expressions
• string.unicode method, just like string.byte but returning a whole unicode codepoint
• string.contains, string.startsWith and string.endsWith methods allow easier and faster performing string ops without having to rely on patterns for simple scenarios
• The json module to support JSON<->table conversions