1 files changed, 150 insertions, 0 deletions
diff --git a/tpl/collections/apply.go b/tpl/collections/apply.go
new file mode 100644
index 000000000..c3c3a297b
--- /dev/null
+++ b/tpl/collections/apply.go
@@ -0,0 +1,150 @@
+// 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 (
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/gohugoio/hugo/tpl"
+)
+
+// Apply takes a map, array, or slice and returns a new slice with the function fname applied over it.
+func (ns *Namespace) Apply(seq interface{}, fname string, args ...interface{}) (interface{}, error) {
+	if seq == nil {
+		return make([]interface{}, 0), nil
+	}
+
+	if fname == "apply" {
+		return nil, errors.New("can't apply myself (no turtles allowed)")
+	}
+
+	seqv := reflect.ValueOf(seq)
+	seqv, isNil := indirect(seqv)
+	if isNil {
+		return nil, errors.New("can't iterate over a nil value")
+	}
+
+	fnv, found := ns.lookupFunc(fname)
+	if !found {
+		return nil, errors.New("can't find function " + fname)
+	}
+
+	// fnv := reflect.ValueOf(fn)
+
+	switch seqv.Kind() {
+	case reflect.Array, reflect.Slice:
+		r := make([]interface{}, seqv.Len())
+		for i := 0; i < seqv.Len(); i++ {
+			vv := seqv.Index(i)
+
+			vvv, err := applyFnToThis(fnv, vv, args...)
+
+			if err != nil {
+				return nil, err
+			}
+
+			r[i] = vvv.Interface()
+		}
+
+		return r, nil
+	default:
+		return nil, fmt.Errorf("can't apply over %v", seq)
+	}
+}
+
+func applyFnToThis(fn, this reflect.Value, args ...interface{}) (reflect.Value, error) {
+	n := make([]reflect.Value, len(args))
+	for i, arg := range args {
+		if arg == "." {
+			n[i] = this
+		} else {
+			n[i] = reflect.ValueOf(arg)
+		}
+	}
+
+	num := fn.Type().NumIn()
+
+	if fn.Type().IsVariadic() {
+		num--
+	}
+
+	// TODO(bep) see #1098 - also see template_tests.go
+	/*if len(args) < num {
+		return reflect.ValueOf(nil), errors.New("Too few arguments")
+	} else if len(args) > num {
+		return reflect.ValueOf(nil), errors.New("Too many arguments")
+	}*/
+
+	for i := 0; i < num; i++ {
+		// AssignableTo reports whether xt is assignable to type targ.
+		if xt, targ := n[i].Type(), fn.Type().In(i); !xt.AssignableTo(targ) {
+			return reflect.ValueOf(nil), errors.New("called apply using " + xt.String() + " as type " + targ.String())
+		}
+	}
+
+	res := fn.Call(n)
+
+	if len(res) == 1 || res[1].IsNil() {
+		return res[0], nil
+	}
+	return reflect.ValueOf(nil), res[1].Interface().(error)
+}
+
+func (ns *Namespace) lookupFunc(fname string) (reflect.Value, bool) {
+	if !strings.ContainsRune(fname, '.') {
+		templ, ok := ns.deps.Tmpl.(tpl.TemplateFuncsGetter)
+		if !ok {
+			panic("Needs a tpl.TemplateFuncsGetter")
+		}
+		fm := templ.GetFuncs()
+		fn, found := fm[fname]
+		if !found {
+			return reflect.Value{}, false
+		}
+
+		return reflect.ValueOf(fn), true
+	}
+
+	ss := strings.SplitN(fname, ".", 2)
+
+	// namespace
+	nv, found := ns.lookupFunc(ss[0])
+	if !found {
+		return reflect.Value{}, false
+	}
+
+	// method
+	m := nv.MethodByName(ss[1])
+	// if reflect.DeepEqual(m, reflect.Value{}) {
+	if m.Kind() == reflect.Invalid {
+		return reflect.Value{}, false
+	}
+	return m, true
+}
+
+// indirect is taken from 'text/template/exec.go'
+func indirect(v reflect.Value) (rv reflect.Value, isNil bool) {
+	for ; v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface; v = v.Elem() {
+		if v.IsNil() {
+			return v, true
+		}
+		if v.Kind() == reflect.Interface && v.NumMethod() > 0 {
+			break
+		}
+	}
+	return v, false
+}