From 6357d3b3f3522cb2e39d2bae8cf41a3ae31c1a34 Mon Sep 17 00:00:00 2001
From: Jack Christensen <jack@jackchristensen.com>
Date: Sat, 2 May 2020 17:31:53 -0500
Subject: [PATCH] Avoid extra type assertion on native type Scan path

Before:
BenchmarkConnInfoScanInt4IntoBinaryDecoder-16    	89744814	        12.5 ns/op	       0 B/op	       0 allocs/op
BenchmarkConnInfoScanInt4IntoGoInt32-16          	27688370	        41.1 ns/op	       0 B/op	       0 allocs/op

After:
BenchmarkConnInfoScanInt4IntoBinaryDecoder-16    	88181061	        12.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkConnInfoScanInt4IntoGoInt32-16          	30402768	        36.8 ns/op	       0 B/op	       0 allocs/op
---
 pgtype.go | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/pgtype.go b/pgtype.go
index 914e02d2..f7dc1379 100644
--- a/pgtype.go
+++ b/pgtype.go
@@ -337,12 +337,17 @@ func (ci *ConnInfo) DeepCopy() *ConnInfo {
 }
 
 func (ci *ConnInfo) Scan(oid uint32, formatCode int16, buf []byte, dest interface{}) error {
-	if dest, ok := dest.(BinaryDecoder); ok && formatCode == BinaryFormatCode {
-		return dest.DecodeBinary(ci, buf)
-	}
-
-	if dest, ok := dest.(TextDecoder); ok && formatCode == TextFormatCode {
-		return dest.DecodeText(ci, buf)
+	switch formatCode {
+	case BinaryFormatCode:
+		if dest, ok := dest.(BinaryDecoder); ok {
+			return dest.DecodeBinary(ci, buf)
+		}
+	case TextFormatCode:
+		if dest, ok := dest.(TextDecoder); ok {
+			return dest.DecodeText(ci, buf)
+		}
+	default:
+		return errors.Errorf("unknown format code: %v", formatCode)
 	}
 
 	if dt, ok := ci.DataTypeForOID(oid); ok {
@@ -366,8 +371,6 @@ func (ci *ConnInfo) Scan(oid uint32, formatCode int16, buf []byte, dest interfac
 			} else {
 				return errors.Errorf("%T is not a pgtype.BinaryDecoder", value)
 			}
-		default:
-			return errors.Errorf("unknown format code: %v", formatCode)
 		}
 
 		if scanner, ok := dest.(sql.Scanner); ok {