Move not null Oid to pgtype

In preparation to ConnInfo implementation.

pgtype/oid_value.go

@@ -0,0 +1,45 @@
+package pgtype
+
+import (
+	"io"
+)
+
+// OidValue (Object Identifier Type) is, according to
+// https://www.postgresql.org/docs/current/static/datatype-OidValue.html, used
+// internally by PostgreSQL as a primary key for various system tables. It is
+// currently implemented as an unsigned four-byte integer. Its definition can be
+// found in src/include/postgres_ext.h in the PostgreSQL sources.
+type OidValue pguint32
+
+// Set converts from src to dst. Note that as OidValue is not a general
+// number type Set does not do automatic type conversion as other number
+// types do.
+func (dst *OidValue) Set(src interface{}) error {
+	return (*pguint32)(dst).Set(src)
+}
+
+func (dst *OidValue) Get() interface{} {
+	return (*pguint32)(dst).Get()
+}
+
+// AssignTo assigns from src to dst. Note that as OidValue is not a general number
+// type AssignTo does not do automatic type conversion as other number types do.
+func (src *OidValue) AssignTo(dst interface{}) error {
+	return (*pguint32)(src).AssignTo(dst)
+}
+
+func (dst *OidValue) DecodeText(src []byte) error {
+	return (*pguint32)(dst).DecodeText(src)
+}
+
+func (dst *OidValue) DecodeBinary(src []byte) error {
+	return (*pguint32)(dst).DecodeBinary(src)
+}
+
+func (src OidValue) EncodeText(w io.Writer) (bool, error) {
+	return (pguint32)(src).EncodeText(w)
+}
+
+func (src OidValue) EncodeBinary(w io.Writer) (bool, error) {
+	return (pguint32)(src).EncodeBinary(w)
+}