clarify datatype comments and standardize file name

datatype/datatype.go

@@ -0,0 +1,23 @@
+package datatype
+
+import (
+	"reflect"
+)
+
+// Validator returns whether a given value fulfills the datatype
+// and casts the value into a common go type.
+//
+// for example, if a validator checks for upper case strings,
+// whether the value is a []byte, a string or a []rune, if the
+// value matches the validator's checks, it will be cast it into
+// a common go type, say, string.
+type Validator func(value interface{}) (cast interface{}, valid bool)
+
+// T represents a datatype. The Build function returns a Validator if
+// it manages types with the name `typeDefinition` (from the configuration field "type"); else it or returns NIL if the type
+// definition does not match this datatype; the registry is passed to allow recursive datatypes (e.g. slices, structs, etc)
+// The datatype's validator (when input is valid) must return a cast's go type matching the `Type() reflect.Type`
+type T interface {
+	Type() reflect.Type
+	Build(typeDefinition string, registry ...T) Validator
+}

datatype/types.go

@@ -1,15 +0,0 @@
-package datatype
-
-import "reflect"
-
-// Validator returns whether a given value fulfills a datatype
-// and casts the value into a compatible type
-type Validator func(value interface{}) (cast interface{}, valid bool)
-
-// T builds a T from the type definition (from the configuration field "type") and returns NIL if the type
-// definition does not match this T ; the registry is passed for recursive datatypes (e.g. slices, structs, etc)
-// to be able to access other datatypes
-type T interface {
-	Type() reflect.Type
-	Build(typeDefinition string, registry ...T) Validator
-}