Add a guard to the configuration tables to also validate direct assignments

Currently, even with the new config-structure, it is still possible to directly assign wrong values to valid fields. For example:

mirror.mirrorMode = true would not throw an error until the value is used.

Now LUA provides two metamethods to react to index manipulations:

__index is called when an index should be read that does not exist.
__newindex is called if one wants to write to an index that does not exist.

Both cases are not called anymore once an index of the name has been assign to the table.

Possible solutions

One idea would be to wrap the actual configuration table yet in another table. This proxy table would stay empty. Instead, all reads or assigns call the tables metamethods __index and __newindex. These methods would then call the guarded functions on the config table, like "setField". This solution would basically add a fourth level to the config (DefaultBase -> DefaultFeature -> Config -> Proxy).

Another suggestion from @gynt would be to instead use a bit of name manipulation and add underscores to the actual values. Example:

Test = {
  new = function(self) 
    local o = {_active = false};
    setmetatable(o, self);
    return o;
  end, 
  __index = function(self, k) 
    print("get: " .. k); 
    return rawget(self, "_" .. k); 
  end, 
  __newindex = function(self, k, v) 
    print("set:" .. k); 
    rawset(self, "_" .. k, v); 
  end
}

t = Test:new()
print(t.active)
t.active = true
print(t.active)

This method would still allow intentional direct access (by using "_" + parameter name), but will otherwise protect the variable from being accidentally set.

gynt / stronghold-mapeditortools

Add a guard to the configuration tables to also validate direct assignments #9