compare, hugolib, tpl: Add Eqer interface

And use it in `eq` and `ne` so `Page` values can be compared directly in the templates without thinking about it being a `Page` or a `PageOutput` wrapper.

Fixes #3807

1 files changed, 21 insertions, 0 deletions

diff --git a/compare/eq.go b/compare/eq.go
new file mode 100644
index 000000000..6120c0bf2
--- /dev/null
+++ b/compare/eq.go
@@ -0,0 +1,21 @@
+// Copyright 2017-present The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package compare
+
+// Eqer can be used to determine if this value is equal to the other.
+// The semantics of equals is that the two value are interchangeable
+// in the Hugo templates.
+type Eqer interface {
+	Eq(other interface{}) bool
+}