remove const from default field value

lib/core/httpconnection/caching.v

@@ -5,15 +5,16 @@ import json
 import net.http { Method }
 
 // https://cassiomolin.com/2016/09/09/which-http-status-codes-are-cacheable/
-const default_cacheable_codes = [200, 203, 204, 206, 300, 404, 405, 410, 414, 501]
-
-const unsafe_http_methods = [Method.put, .patch, .post, .delete]
+const (
+	default_cacheable_codes = [200, 203, 204, 206, 300, 404, 405, 410, 414, 501]
+	unsafe_http_methods = [Method.put, .patch, .post, .delete]
+)
 
 pub struct CacheConfig {
 pub mut:
 	key               string // as used to identity in redis
 	allowable_methods []Method = [.get, .head]
-	allowable_codes   []int    = default_cacheable_codes
+	allowable_codes   []int    = [200, 203, 204, 206, 300, 404, 405, 410, 414, 501] // TODO: produces v compiler error to use const
 	disable           bool     = true // default cache is not working
 	expire_after      int      = 3600 // default expire_after is 1h
 	match_headers     bool // cache the request header to be matched later