fix ineffectual assignments

Warnings are produced by "ineffassign" linter

altsrc/json_source_context.go

@@ -79,9 +79,9 @@ func (x *jsonSource) Duration(name string) (time.Duration, error) {
 	if err != nil {
 		return 0, err
 	}
-	v, ok := (time.Duration)(0), false
-	if v, ok = i.(time.Duration); !ok {
-		return v, fmt.Errorf("unexpected type %T for %q", i, name)
+	v, ok := i.(time.Duration)
+	if !ok {
+		return 0, fmt.Errorf("unexpected type %T for %q", i, name)
 	}
 	return v, nil
 }
@@ -91,9 +91,9 @@ func (x *jsonSource) Float64(name string) (float64, error) {
 	if err != nil {
 		return 0, err
 	}
-	v, ok := (float64)(0), false
-	if v, ok = i.(float64); !ok {
-		return v, fmt.Errorf("unexpected type %T for %q", i, name)
+	v, ok := i.(float64)
+	if !ok {
+		return 0, fmt.Errorf("unexpected type %T for %q", i, name)
 	}
 	return v, nil
 }
@@ -103,9 +103,9 @@ func (x *jsonSource) String(name string) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	v, ok := "", false
-	if v, ok = i.(string); !ok {
-		return v, fmt.Errorf("unexpected type %T for %q", i, name)
+	v, ok := i.(string)
+	if !ok {
+		return "", fmt.Errorf("unexpected type %T for %q", i, name)
 	}
 	return v, nil
 }
@@ -161,9 +161,9 @@ func (x *jsonSource) Generic(name string) (cli.Generic, error) {
 	if err != nil {
 		return nil, err
 	}
-	v, ok := (cli.Generic)(nil), false
-	if v, ok = i.(cli.Generic); !ok {
-		return v, fmt.Errorf("unexpected type %T for %q", i, name)
+	v, ok := i.(cli.Generic)
+	if !ok {
+		return nil, fmt.Errorf("unexpected type %T for %q", i, name)
 	}
 	return v, nil
 }
@@ -173,9 +173,9 @@ func (x *jsonSource) Bool(name string) (bool, error) {
 	if err != nil {
 		return false, err
 	}
-	v, ok := false, false
-	if v, ok = i.(bool); !ok {
-		return v, fmt.Errorf("unexpected type %T for %q", i, name)
+	v, ok := i.(bool)
+	if !ok {
+		return false, fmt.Errorf("unexpected type %T for %q", i, name)
 	}
 	return v, nil
 }

altsrc/map_input_source_test.go

@@ -20,6 +20,6 @@ func TestMapDuration(t *testing.T) {
 	d, err = inputSource.Duration("duration_of_string_type")
 	expect(t, time.Minute, d)
 	expect(t, nil, err)
-	d, err = inputSource.Duration("duration_of_int_type")
+	_, err = inputSource.Duration("duration_of_int_type")
 	refute(t, nil, err)
 }