Add Component Negation

Fixes #32

concord/components.lua

@@ -1,12 +1,11 @@
 --- Container for registered ComponentClasses
 -- @module Components
 
-local PATH = (...):gsub('%.[^%.]+$', '')
-
-local Type = require(PATH..".type")
-
 local Components = {}
 
+Components.__REJECT_PREFIX = "!"
+Components.__REJECT_MATCH = "^(%"..Components.__REJECT_PREFIX.."?)(.+)"
+
 --- Returns true if the containter has the ComponentClass with the specified name
 -- @string name Name of the ComponentClass to check
 -- @treturn boolean
@@ -14,22 +13,43 @@ function Components.has(name)
    return rawget(Components, name) and true or false
 end
 
+--- Prefix a component's name with the currently set Reject Prefix
+-- @string name Name of the ComponentClass to reject
+-- @treturn string
+function Components.reject(name)
+   local ok, err = Components.try(name)
+
+   if not ok then error(err, 2) end
+
+   return Components.__REJECT_PREFIX..name
+end
+
 --- Returns true and the ComponentClass if one was registered with the specified name
 -- or false and an error otherwise
 -- @string name Name of the ComponentClass to check
+-- @boolean acceptRejected Whether to accept names prefixed with the Reject Prefix.
 -- @treturn boolean
 -- @treturn Component or error string
-function Components.try(name)
+-- @treturn true if acceptRejected was true and the name had the Reject Prefix, false otherwise.
+function Components.try(name, acceptRejected)
    if type(name) ~= "string" then
       return false, "ComponentsClass name is expected to be a string, got "..type(name)..")"
    end
 
+   local rejected = false
+   if acceptRejected then
+      local prefix
+      prefix, name = string.match(name, Components.__REJECT_MATCH)
+
+      rejected = prefix ~= "" and name
+   end
+
    local value = rawget(Components, name)
    if not value then
       return false, "ComponentClass '"..name.."' does not exist / was not registered"
    end
 
-   return true, value
+   return true, value, rejected
 end
 
 --- Returns the ComponentClass with the specified name