tpl: Add reflect namespace

Add a reflect namespace that offers a two boolean functions for
testing if a value is a map or slice.

Fixes #4081

tpl/reflect/init.go

@@ -0,0 +1,50 @@
+// Copyright 2018 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 reflect
+
+import (
+	"github.com/gohugoio/hugo/deps"
+	"github.com/gohugoio/hugo/tpl/internal"
+)
+
+const name = "reflect"
+
+func init() {
+	f := func(d *deps.Deps) *internal.TemplateFuncsNamespace {
+		ctx := New()
+
+		ns := &internal.TemplateFuncsNamespace{
+			Name:    name,
+			Context: func(args ...interface{}) interface{} { return ctx },
+		}
+
+		ns.AddMethodMapping(ctx.IsMap,
+			nil,
+			[][2]string{
+				{`{{ if reflect.IsMap (dict "a" 1) }}Map{{ end }}`, `Map`},
+			},
+		)
+
+		ns.AddMethodMapping(ctx.IsSlice,
+			nil,
+			[][2]string{
+				{`{{ if reflect.IsSlice (slice 1 2 3) }}Slice{{ end }}`, `Slice`},
+			},
+		)
+
+		return ns
+	}
+
+	internal.AddTemplateFuncsNamespace(f)
+}