tpl/collections: Fix In function for JSON arrays

Fixes #1468

tpl/collections/reflect_helpers.go

@@ -0,0 +1,64 @@
+// Copyright 2017 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 collections
+
+import (
+	"reflect"
+)
+
+func numberToFloat(v reflect.Value) float64 {
+	switch kind := v.Kind(); {
+	case isFloat(kind):
+		return v.Float()
+	case isInt(kind):
+		return float64(v.Int())
+	case isUInt(kind):
+		return float64(v.Uint())
+	case kind == reflect.Interface:
+		return numberToFloat(v.Elem())
+	default:
+		panic("Invalid type in numberToFloat")
+	}
+}
+
+func isNumber(kind reflect.Kind) bool {
+	return isInt(kind) || isUInt(kind) || isFloat(kind)
+}
+
+func isInt(kind reflect.Kind) bool {
+	switch kind {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return true
+	default:
+		return false
+	}
+}
+
+func isUInt(kind reflect.Kind) bool {
+	switch kind {
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		return true
+	default:
+		return false
+	}
+}
+
+func isFloat(kind reflect.Kind) bool {
+	switch kind {
+	case reflect.Float32, reflect.Float64:
+		return true
+	default:
+		return false
+	}
+}