Ports the decl repository. (#8460)

code/datums/repositories/decls.dm

@@ -0,0 +1,51 @@
+/var/repository/decls/decls_repository = new()
+
+/repository/decls
+	var/list/fetched_decls
+	var/list/fetched_decl_types
+	var/list/fetched_decl_subtypes
+
+/repository/decls/New()
+	..()
+	fetched_decls = list()
+	fetched_decl_types = list()
+	fetched_decl_subtypes = list()
+
+/repository/decls/proc/get_decl(var/decl_type)
+	. = fetched_decls[decl_type]
+	if(!.)
+		. = new decl_type()
+		fetched_decls[decl_type] = .
+
+		var/decl/decl = .
+		if(istype(decl))
+			decl.Initialize()
+
+/repository/decls/proc/get_decls(var/list/decl_types)
+	. = list()
+	for(var/decl_type in decl_types)
+		.[decl_type] = get_decl(decl_type)
+
+/repository/decls/proc/get_decls_unassociated(var/list/decl_types)
+	. = list()
+	for(var/decl_type in decl_types)
+		. += get_decl(decl_type)
+
+/repository/decls/proc/get_decls_of_type(var/decl_prototype)
+	. = fetched_decl_types[decl_prototype]
+	if(!.)
+		. = get_decls(typesof(decl_prototype))
+		fetched_decl_types[decl_prototype] = .
+
+/repository/decls/proc/get_decls_of_subtype(var/decl_prototype)
+	. = fetched_decl_subtypes[decl_prototype]
+	if(!.)
+		. = get_decls(subtypesof(decl_prototype))
+		fetched_decl_subtypes[decl_prototype] = .
+
+/decl/proc/Initialize()
+	return
+
+/decl/Destroy()
+	SHOULD_CALL_PARENT(FALSE)
+	return QDEL_HINT_LETMELIVE // Prevents Decl destruction