Add a newScratch template func

Fixes #4685

14 files changed, 319 insertions, 231 deletions

diff --git a/hugolib/scratch.go b/common/maps/scratch.go
index 37ed5df35..d00971435 100644
--- a/hugolib/scratch.go
+++ b/common/maps/scratch.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,14 +11,14 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package hugolib
+package maps
 
 import (
 	"reflect"
 	"sort"
 	"sync"
 
-	"github.com/gohugoio/hugo/tpl/math"
+	"github.com/gohugoio/hugo/common/math"
 )
 
 // Scratch is a writable context used for stateful operations in Page/Node rendering.
@@ -130,6 +130,6 @@ func (c *Scratch) GetSortedMapValues(key string) interface{} {
 	return sortedArray
 }
 
-func newScratch() *Scratch {
+func NewScratch() *Scratch {
 	return &Scratch{values: make(map[string]interface{})}
 }
diff --git a/hugolib/scratch_test.go b/common/maps/scratch_test.go
index 5ec2b89c8..8397ba830 100644
--- a/hugolib/scratch_test.go
+++ b/common/maps/scratch_test.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package hugolib
+package maps
 
 import (
 	"reflect"
@@ -23,7 +23,7 @@ import (
 
 func TestScratchAdd(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 	scratch.Add("int1", 10)
 	scratch.Add("int1", 20)
 	scratch.Add("int2", 20)
@@ -53,7 +53,7 @@ func TestScratchAdd(t *testing.T) {
 
 func TestScratchAddSlice(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 
 	_, err := scratch.Add("intSlice", []int{1, 2})
 	assert.Nil(t, err)
@@ -82,14 +82,14 @@ func TestScratchAddSlice(t *testing.T) {
 
 func TestScratchSet(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 	scratch.Set("key", "val")
 	assert.Equal(t, "val", scratch.Get("key"))
 }
 
 func TestScratchDelete(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 	scratch.Set("key", "val")
 	scratch.Delete("key")
 	scratch.Add("key", "Lucy Parsons")
@@ -99,7 +99,7 @@ func TestScratchDelete(t *testing.T) {
 // Issue #2005
 func TestScratchInParallel(t *testing.T) {
 	var wg sync.WaitGroup
-	scratch := newScratch()
+	scratch := NewScratch()
 	key := "counter"
 	scratch.Set(key, int64(1))
 	for i := 1; i <= 10; i++ {
@@ -133,7 +133,7 @@ func TestScratchInParallel(t *testing.T) {
 
 func TestScratchGet(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 	nothing := scratch.Get("nothing")
 	if nothing != nil {
 		t.Errorf("Should not return anything, but got %v", nothing)
@@ -142,7 +142,7 @@ func TestScratchGet(t *testing.T) {
 
 func TestScratchSetInMap(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 	scratch.SetInMap("key", "lux", "Lux")
 	scratch.SetInMap("key", "abc", "Abc")
 	scratch.SetInMap("key", "zyx", "Zyx")
@@ -153,7 +153,7 @@ func TestScratchSetInMap(t *testing.T) {
 
 func TestScratchGetSortedMapValues(t *testing.T) {
 	t.Parallel()
-	scratch := newScratch()
+	scratch := NewScratch()
 	nothing := scratch.GetSortedMapValues("nothing")
 	if nothing != nil {
 		t.Errorf("Should not return anything, but got %v", nothing)
@@ -161,7 +161,7 @@ func TestScratchGetSortedMapValues(t *testing.T) {
 }
 
 func BenchmarkScratchGet(b *testing.B) {
-	scratch := newScratch()
+	scratch := NewScratch()
 	scratch.Add("A", 1)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
diff --git a/common/math/math.go b/common/math/math.go
new file mode 100644
index 000000000..3c5ef1f9d
--- /dev/null
+++ b/common/math/math.go
@@ -0,0 +1,135 @@
+// 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 math
+
+import (
+	"errors"
+	"reflect"
+)
+
+// DoArithmetic performs arithmetic operations (+,-,*,/) using reflection to
+// determine the type of the two terms.
+func DoArithmetic(a, b interface{}, op rune) (interface{}, error) {
+	av := reflect.ValueOf(a)
+	bv := reflect.ValueOf(b)
+	var ai, bi int64
+	var af, bf float64
+	var au, bu uint64
+	switch av.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		ai = av.Int()
+		switch bv.Kind() {
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			bi = bv.Int()
+		case reflect.Float32, reflect.Float64:
+			af = float64(ai) // may overflow
+			ai = 0
+			bf = bv.Float()
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			bu = bv.Uint()
+			if ai >= 0 {
+				au = uint64(ai)
+				ai = 0
+			} else {
+				bi = int64(bu) // may overflow
+				bu = 0
+			}
+		default:
+			return nil, errors.New("Can't apply the operator to the values")
+		}
+	case reflect.Float32, reflect.Float64:
+		af = av.Float()
+		switch bv.Kind() {
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			bf = float64(bv.Int()) // may overflow
+		case reflect.Float32, reflect.Float64:
+			bf = bv.Float()
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			bf = float64(bv.Uint()) // may overflow
+		default:
+			return nil, errors.New("Can't apply the operator to the values")
+		}
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		au = av.Uint()
+		switch bv.Kind() {
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			bi = bv.Int()
+			if bi >= 0 {
+				bu = uint64(bi)
+				bi = 0
+			} else {
+				ai = int64(au) // may overflow
+				au = 0
+			}
+		case reflect.Float32, reflect.Float64:
+			af = float64(au) // may overflow
+			au = 0
+			bf = bv.Float()
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			bu = bv.Uint()
+		default:
+			return nil, errors.New("Can't apply the operator to the values")
+		}
+	case reflect.String:
+		as := av.String()
+		if bv.Kind() == reflect.String && op == '+' {
+			bs := bv.String()
+			return as + bs, nil
+		}
+		return nil, errors.New("Can't apply the operator to the values")
+	default:
+		return nil, errors.New("Can't apply the operator to the values")
+	}
+
+	switch op {
+	case '+':
+		if ai != 0 || bi != 0 {
+			return ai + bi, nil
+		} else if af != 0 || bf != 0 {
+			return af + bf, nil
+		} else if au != 0 || bu != 0 {
+			return au + bu, nil
+		}
+		return 0, nil
+	case '-':
+		if ai != 0 || bi != 0 {
+			return ai - bi, nil
+		} else if af != 0 || bf != 0 {
+			return af - bf, nil
+		} else if au != 0 || bu != 0 {
+			return au - bu, nil
+		}
+		return 0, nil
+	case '*':
+		if ai != 0 || bi != 0 {
+			return ai * bi, nil
+		} else if af != 0 || bf != 0 {
+			return af * bf, nil
+		} else if au != 0 || bu != 0 {
+			return au * bu, nil
+		}
+		return 0, nil
+	case '/':
+		if bi != 0 {
+			return ai / bi, nil
+		} else if bf != 0 {
+			return af / bf, nil
+		} else if bu != 0 {
+			return au / bu, nil
+		}
+		return nil, errors.New("Can't divide the value by 0")
+	default:
+		return nil, errors.New("There is no such an operation")
+	}
+}
diff --git a/common/math/math_test.go b/common/math/math_test.go
new file mode 100644
index 000000000..613ac3073
--- /dev/null
+++ b/common/math/math_test.go
@@ -0,0 +1,109 @@
+// 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 math
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/alecthomas/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDoArithmetic(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		a      interface{}
+		b      interface{}
+		op     rune
+		expect interface{}
+	}{
+		{3, 2, '+', int64(5)},
+		{3, 2, '-', int64(1)},
+		{3, 2, '*', int64(6)},
+		{3, 2, '/', int64(1)},
+		{3.0, 2, '+', float64(5)},
+		{3.0, 2, '-', float64(1)},
+		{3.0, 2, '*', float64(6)},
+		{3.0, 2, '/', float64(1.5)},
+		{3, 2.0, '+', float64(5)},
+		{3, 2.0, '-', float64(1)},
+		{3, 2.0, '*', float64(6)},
+		{3, 2.0, '/', float64(1.5)},
+		{3.0, 2.0, '+', float64(5)},
+		{3.0, 2.0, '-', float64(1)},
+		{3.0, 2.0, '*', float64(6)},
+		{3.0, 2.0, '/', float64(1.5)},
+		{uint(3), uint(2), '+', uint64(5)},
+		{uint(3), uint(2), '-', uint64(1)},
+		{uint(3), uint(2), '*', uint64(6)},
+		{uint(3), uint(2), '/', uint64(1)},
+		{uint(3), 2, '+', uint64(5)},
+		{uint(3), 2, '-', uint64(1)},
+		{uint(3), 2, '*', uint64(6)},
+		{uint(3), 2, '/', uint64(1)},
+		{3, uint(2), '+', uint64(5)},
+		{3, uint(2), '-', uint64(1)},
+		{3, uint(2), '*', uint64(6)},
+		{3, uint(2), '/', uint64(1)},
+		{uint(3), -2, '+', int64(1)},
+		{uint(3), -2, '-', int64(5)},
+		{uint(3), -2, '*', int64(-6)},
+		{uint(3), -2, '/', int64(-1)},
+		{-3, uint(2), '+', int64(-1)},
+		{-3, uint(2), '-', int64(-5)},
+		{-3, uint(2), '*', int64(-6)},
+		{-3, uint(2), '/', int64(-1)},
+		{uint(3), 2.0, '+', float64(5)},
+		{uint(3), 2.0, '-', float64(1)},
+		{uint(3), 2.0, '*', float64(6)},
+		{uint(3), 2.0, '/', float64(1.5)},
+		{3.0, uint(2), '+', float64(5)},
+		{3.0, uint(2), '-', float64(1)},
+		{3.0, uint(2), '*', float64(6)},
+		{3.0, uint(2), '/', float64(1.5)},
+		{0, 0, '+', 0},
+		{0, 0, '-', 0},
+		{0, 0, '*', 0},
+		{"foo", "bar", '+', "foobar"},
+		{3, 0, '/', false},
+		{3.0, 0, '/', false},
+		{3, 0.0, '/', false},
+		{uint(3), uint(0), '/', false},
+		{3, uint(0), '/', false},
+		{-3, uint(0), '/', false},
+		{uint(3), 0, '/', false},
+		{3.0, uint(0), '/', false},
+		{uint(3), 0.0, '/', false},
+		{3, "foo", '+', false},
+		{3.0, "foo", '+', false},
+		{uint(3), "foo", '+', false},
+		{"foo", 3, '+', false},
+		{"foo", "bar", '-', false},
+		{3, 2, '%', false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := DoArithmetic(test.a, test.b, test.op)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
diff --git a/docs/content/en/functions/scratch.md b/docs/content/en/functions/scratch.md
index 9df78fe43..93a1e426a 100644
--- a/docs/content/en/functions/scratch.md
+++ b/docs/content/en/functions/scratch.md
@@ -22,6 +22,9 @@ aliases: [/extras/scratch/,/doc/scratch/]
 
 In most cases you can do okay without `Scratch`, but due to scoping issues, there are many use cases that aren't solvable in Go Templates without `Scratch`'s help.
 
+`.Scratch` is available as methods on `Page` and `Shortcode`. Since Hugo 0.43 you can also create a locally scoped `Scratch` using the template func `newScratch`.
+
+
 {{% note %}}
 See [this Go issue](https://github.com/golang/go/issues/10608) for the main motivation behind Scratch.
 {{% /note %}}
diff --git a/hugolib/page.go b/hugolib/page.go
index d9a3fe31c..6e21d75ae 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -257,7 +257,7 @@ type Page struct {
 
 	layoutDescriptor output.LayoutDescriptor
 
-	scratch *Scratch
+	scratch *maps.Scratch
 
 	// It would be tempting to use the language set on the Site, but in they way we do
 	// multi-site processing, these values may differ during the initial page processing.
@@ -2052,9 +2052,9 @@ func (p *Page) String() string {
 }
 
 // Scratch returns the writable context associated with this Page.
-func (p *Page) Scratch() *Scratch {
+func (p *Page) Scratch() *maps.Scratch {
 	if p.scratch == nil {
-		p.scratch = newScratch()
+		p.scratch = maps.NewScratch()
 	}
 	return p.scratch
 }
diff --git a/hugolib/page_test.go b/hugolib/page_test.go
index 985373a90..b512a9a5a 100644
--- a/hugolib/page_test.go
+++ b/hugolib/page_test.go
@@ -1830,6 +1830,33 @@ Summary: In Chinese, 好 means good.
 
 }
 
+func TestScratchSite(t *testing.T) {
+	t.Parallel()
+
+	b := newTestSitesBuilder(t)
+	b.WithSimpleConfigFile().WithTemplatesAdded("index.html", `
+{{ .Scratch.Set "b" "bv" }}
+B: {{ .Scratch.Get "b" }}
+`,
+		"shortcodes/scratch.html", `
+{{ .Scratch.Set "c" "cv" }}
+C: {{ .Scratch.Get "c" }}
+`,
+	)
+
+	b.WithContentAdded("scratchme.md", `
+---
+title: Scratch Me!
+---
+
+{{< scratch >}}
+`)
+	b.Build(BuildCfg{})
+
+	b.AssertFileContent("public/index.html", "B: bv")
+	b.AssertFileContent("public/scratchme/index.html", "C: cv")
+}
+
 func BenchmarkParsePage(b *testing.B) {
 	s := newTestSite(b)
 	f, _ := os.Open("testdata/redis.cn.md")
diff --git a/hugolib/shortcode.go b/hugolib/shortcode.go
index c07a5586a..cf5b0ece0 100644
--- a/hugolib/shortcode.go
+++ b/hugolib/shortcode.go
@@ -24,6 +24,7 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/output"
 
 	"github.com/gohugoio/hugo/media"
@@ -45,7 +46,7 @@ type ShortcodeWithPage struct {
 	// this ordinal will represent the position of this shortcode in the page content.
 	Ordinal int
 
-	scratch *Scratch
+	scratch *maps.Scratch
 }
 
 // Site returns information about the current site.
@@ -65,9 +66,9 @@ func (scp *ShortcodeWithPage) RelRef(ref string) (string, error) {
 
 // Scratch returns a scratch-pad scoped for this shortcode. This can be used
 // as a temporary storage for variables, counters etc.
-func (scp *ShortcodeWithPage) Scratch() *Scratch {
+func (scp *ShortcodeWithPage) Scratch() *maps.Scratch {
 	if scp.scratch == nil {
-		scp.scratch = newScratch()
+		scp.scratch = maps.NewScratch()
 	}
 	return scp.scratch
 }
diff --git a/hugolib/site.go b/hugolib/site.go
index df7e66d4a..a749bafd0 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -27,6 +27,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/resource"
 
 	"github.com/gohugoio/hugo/langs"
@@ -1509,7 +1510,7 @@ func (s *Site) resetBuildState() {
 	for _, p := range s.rawAllPages {
 		p.subSections = Pages{}
 		p.parent = nil
-		p.scratch = newScratch()
+		p.scratch = maps.NewScratch()
 		p.mainPageOutput = nil
 	}
 }
diff --git a/tpl/collections/collections.go b/tpl/collections/collections.go
index dd418d7d2..51bc5c796 100644
--- a/tpl/collections/collections.go
+++ b/tpl/collections/collections.go
@@ -23,6 +23,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/helpers"
@@ -650,3 +651,9 @@ func (ns *Namespace) Uniq(l interface{}) (interface{}, error) {
 func (ns *Namespace) KeyVals(key interface{}, vals ...interface{}) (types.KeyValues, error) {
 	return types.KeyValues{Key: key, Values: vals}, nil
 }
+
+// NewScratch creates a new Scratch which can be used to store values in a
+// thread safe way.
+func (ns *Namespace) NewScratch() *maps.Scratch {
+	return maps.NewScratch()
+}
diff --git a/tpl/collections/init.go b/tpl/collections/init.go
index 91b0dea01..b986b3b42 100644
--- a/tpl/collections/init.go
+++ b/tpl/collections/init.go
@@ -144,6 +144,14 @@ func init() {
 				{`{{ seq 3 }}`, `[1 2 3]`},
 			},
 		)
+
+		ns.AddMethodMapping(ctx.NewScratch,
+			[]string{"newScratch"},
+			[][2]string{
+				{`{{ $scratch := newScratch }}{{ $scratch.Add "b" 2 }}{{ $scratch.Add "b" 2 }}{{ $scratch.Get "b" }}`, `4`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.Uniq,
 			[]string{"uniq"},
 			[][2]string{
diff --git a/tpl/math/math.go b/tpl/math/math.go
index 534f7f284..fcc6abc3d 100644
--- a/tpl/math/math.go
+++ b/tpl/math/math.go
@@ -16,7 +16,8 @@ package math
 import (
 	"errors"
 	"math"
-	"reflect"
+
+	_math "github.com/gohugoio/hugo/common/math"
 
 	"github.com/spf13/cast"
 )
@@ -31,7 +32,7 @@ type Namespace struct{}
 
 // Add adds two numbers.
 func (ns *Namespace) Add(a, b interface{}) (interface{}, error) {
-	return DoArithmetic(a, b, '+')
+	return _math.DoArithmetic(a, b, '+')
 }
 
 // Ceil returns the least integer value greater than or equal to x.
@@ -46,7 +47,7 @@ func (ns *Namespace) Ceil(x interface{}) (float64, error) {
 
 // Div divides two numbers.
 func (ns *Namespace) Div(a, b interface{}) (interface{}, error) {
-	return DoArithmetic(a, b, '/')
+	return _math.DoArithmetic(a, b, '/')
 }
 
 // Floor returns the greatest integer value less than or equal to x.
@@ -98,7 +99,7 @@ func (ns *Namespace) ModBool(a, b interface{}) (bool, error) {
 
 // Mul multiplies two numbers.
 func (ns *Namespace) Mul(a, b interface{}) (interface{}, error) {
-	return DoArithmetic(a, b, '*')
+	return _math.DoArithmetic(a, b, '*')
 }
 
 // Round returns the nearest integer, rounding half away from zero.
@@ -113,121 +114,5 @@ func (ns *Namespace) Round(x interface{}) (float64, error) {
 
 // Sub subtracts two numbers.
 func (ns *Namespace) Sub(a, b interface{}) (interface{}, error) {
-	return DoArithmetic(a, b, '-')
-}
-
-// DoArithmetic performs arithmetic operations (+,-,*,/) using reflection to
-// determine the type of the two terms.
-func DoArithmetic(a, b interface{}, op rune) (interface{}, error) {
-	av := reflect.ValueOf(a)
-	bv := reflect.ValueOf(b)
-	var ai, bi int64
-	var af, bf float64
-	var au, bu uint64
-	switch av.Kind() {
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		ai = av.Int()
-		switch bv.Kind() {
-		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-			bi = bv.Int()
-		case reflect.Float32, reflect.Float64:
-			af = float64(ai) // may overflow
-			ai = 0
-			bf = bv.Float()
-		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-			bu = bv.Uint()
-			if ai >= 0 {
-				au = uint64(ai)
-				ai = 0
-			} else {
-				bi = int64(bu) // may overflow
-				bu = 0
-			}
-		default:
-			return nil, errors.New("Can't apply the operator to the values")
-		}
-	case reflect.Float32, reflect.Float64:
-		af = av.Float()
-		switch bv.Kind() {
-		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-			bf = float64(bv.Int()) // may overflow
-		case reflect.Float32, reflect.Float64:
-			bf = bv.Float()
-		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-			bf = float64(bv.Uint()) // may overflow
-		default:
-			return nil, errors.New("Can't apply the operator to the values")
-		}
-	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-		au = av.Uint()
-		switch bv.Kind() {
-		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-			bi = bv.Int()
-			if bi >= 0 {
-				bu = uint64(bi)
-				bi = 0
-			} else {
-				ai = int64(au) // may overflow
-				au = 0
-			}
-		case reflect.Float32, reflect.Float64:
-			af = float64(au) // may overflow
-			au = 0
-			bf = bv.Float()
-		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-			bu = bv.Uint()
-		default:
-			return nil, errors.New("Can't apply the operator to the values")
-		}
-	case reflect.String:
-		as := av.String()
-		if bv.Kind() == reflect.String && op == '+' {
-			bs := bv.String()
-			return as + bs, nil
-		}
-		return nil, errors.New("Can't apply the operator to the values")
-	default:
-		return nil, errors.New("Can't apply the operator to the values")
-	}
-
-	switch op {
-	case '+':
-		if ai != 0 || bi != 0 {
-			return ai + bi, nil
-		} else if af != 0 || bf != 0 {
-			return af + bf, nil
-		} else if au != 0 || bu != 0 {
-			return au + bu, nil
-		}
-		return 0, nil
-	case '-':
-		if ai != 0 || bi != 0 {
-			return ai - bi, nil
-		} else if af != 0 || bf != 0 {
-			return af - bf, nil
-		} else if au != 0 || bu != 0 {
-			return au - bu, nil
-		}
-		return 0, nil
-	case '*':
-		if ai != 0 || bi != 0 {
-			return ai * bi, nil
-		} else if af != 0 || bf != 0 {
-			return af * bf, nil
-		} else if au != 0 || bu != 0 {
-			return au * bu, nil
-		}
-		return 0, nil
-	case '/':
-		if bi != 0 {
-			return ai / bi, nil
-		} else if bf != 0 {
-			return af / bf, nil
-		} else if bu != 0 {
-			return au / bu, nil
-		}
-		return nil, errors.New("Can't divide the value by 0")
-	default:
-		return nil, errors.New("There is no such an operation")
-	}
+	return _math.DoArithmetic(a, b, '-')
 }
diff --git a/tpl/math/math_test.go b/tpl/math/math_test.go
index 97acfaeba..f2e6236af 100644
--- a/tpl/math/math_test.go
+++ b/tpl/math/math_test.go
@@ -56,93 +56,6 @@ func TestBasicNSArithmetic(t *testing.T) {
 	}
 }
 
-func TestDoArithmetic(t *testing.T) {
-	t.Parallel()
-
-	for i, test := range []struct {
-		a      interface{}
-		b      interface{}
-		op     rune
-		expect interface{}
-	}{
-		{3, 2, '+', int64(5)},
-		{3, 2, '-', int64(1)},
-		{3, 2, '*', int64(6)},
-		{3, 2, '/', int64(1)},
-		{3.0, 2, '+', float64(5)},
-		{3.0, 2, '-', float64(1)},
-		{3.0, 2, '*', float64(6)},
-		{3.0, 2, '/', float64(1.5)},
-		{3, 2.0, '+', float64(5)},
-		{3, 2.0, '-', float64(1)},
-		{3, 2.0, '*', float64(6)},
-		{3, 2.0, '/', float64(1.5)},
-		{3.0, 2.0, '+', float64(5)},
-		{3.0, 2.0, '-', float64(1)},
-		{3.0, 2.0, '*', float64(6)},
-		{3.0, 2.0, '/', float64(1.5)},
-		{uint(3), uint(2), '+', uint64(5)},
-		{uint(3), uint(2), '-', uint64(1)},
-		{uint(3), uint(2), '*', uint64(6)},
-		{uint(3), uint(2), '/', uint64(1)},
-		{uint(3), 2, '+', uint64(5)},
-		{uint(3), 2, '-', uint64(1)},
-		{uint(3), 2, '*', uint64(6)},
-		{uint(3), 2, '/', uint64(1)},
-		{3, uint(2), '+', uint64(5)},
-		{3, uint(2), '-', uint64(1)},
-		{3, uint(2), '*', uint64(6)},
-		{3, uint(2), '/', uint64(1)},
-		{uint(3), -2, '+', int64(1)},
-		{uint(3), -2, '-', int64(5)},
-		{uint(3), -2, '*', int64(-6)},
-		{uint(3), -2, '/', int64(-1)},
-		{-3, uint(2), '+', int64(-1)},
-		{-3, uint(2), '-', int64(-5)},
-		{-3, uint(2), '*', int64(-6)},
-		{-3, uint(2), '/', int64(-1)},
-		{uint(3), 2.0, '+', float64(5)},
-		{uint(3), 2.0, '-', float64(1)},
-		{uint(3), 2.0, '*', float64(6)},
-		{uint(3), 2.0, '/', float64(1.5)},
-		{3.0, uint(2), '+', float64(5)},
-		{3.0, uint(2), '-', float64(1)},
-		{3.0, uint(2), '*', float64(6)},
-		{3.0, uint(2), '/', float64(1.5)},
-		{0, 0, '+', 0},
-		{0, 0, '-', 0},
-		{0, 0, '*', 0},
-		{"foo", "bar", '+', "foobar"},
-		{3, 0, '/', false},
-		{3.0, 0, '/', false},
-		{3, 0.0, '/', false},
-		{uint(3), uint(0), '/', false},
-		{3, uint(0), '/', false},
-		{-3, uint(0), '/', false},
-		{uint(3), 0, '/', false},
-		{3.0, uint(0), '/', false},
-		{uint(3), 0.0, '/', false},
-		{3, "foo", '+', false},
-		{3.0, "foo", '+', false},
-		{uint(3), "foo", '+', false},
-		{"foo", 3, '+', false},
-		{"foo", "bar", '-', false},
-		{3, 2, '%', false},
-	} {
-		errMsg := fmt.Sprintf("[%d] %v", i, test)
-
-		result, err := DoArithmetic(test.a, test.b, test.op)
-
-		if b, ok := test.expect.(bool); ok && !b {
-			require.Error(t, err, errMsg)
-			continue
-		}
-
-		require.NoError(t, err, errMsg)
-		assert.Equal(t, test.expect, result, errMsg)
-	}
-}
-
 func TestCeil(t *testing.T) {
 	t.Parallel()
 
diff --git a/tpl/tplimpl/template_funcs_test.go b/tpl/tplimpl/template_funcs_test.go
index 341be805a..8594c67a4 100644
--- a/tpl/tplimpl/template_funcs_test.go
+++ b/tpl/tplimpl/template_funcs_test.go
@@ -125,7 +125,6 @@ func TestTemplateFuncsExamples(t *testing.T) {
 			}
 		}
 	}
-
 }
 
 // TODO(bep) it would be dandy to put this one into the partials package, but