all: use strings.Builder (#163)

Fixes #95

7 files changed, 40 insertions, 44 deletions

diff --git a/starlark/eval.go b/starlark/eval.go
index 8268270..11ebbe1 100644
--- a/starlark/eval.go
+++ b/starlark/eval.go
@@ -5,7 +5,6 @@
 package starlark
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -88,14 +87,14 @@ func (d StringDict) Keys() []string {
 }
 
 func (d StringDict) String() string {
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	buf.WriteByte('{')
 	sep := ""
 	for _, name := range d.Keys() {
 		buf.WriteString(sep)
 		buf.WriteString(name)
 		buf.WriteString(": ")
-		writeValue(&buf, d[name], nil)
+		writeValue(buf, d[name], nil)
 		sep = ", "
 	}
 	buf.WriteByte('}')
@@ -175,14 +174,14 @@ func (e *EvalError) Error() string { return e.Msg }
 // Backtrace returns a user-friendly error message describing the stack
 // of calls that led to this error.
 func (e *EvalError) Backtrace() string {
-	var buf bytes.Buffer
-	e.Frame.WriteBacktrace(&buf)
-	fmt.Fprintf(&buf, "Error: %s", e.Msg)
+	buf := new(strings.Builder)
+	e.Frame.WriteBacktrace(buf)
+	fmt.Fprintf(buf, "Error: %s", e.Msg)
 	return buf.String()
 }
 
 // WriteBacktrace writes a user-friendly description of the stack to buf.
-func (fr *Frame) WriteBacktrace(out *bytes.Buffer) {
+func (fr *Frame) WriteBacktrace(out *strings.Builder) {
 	fmt.Fprintf(out, "Traceback (most recent call last):\n")
 	var print func(fr *Frame)
 	print = func(fr *Frame) {
@@ -1302,7 +1301,7 @@ func (is *intset) len() int {
 
 // https://github.com/google/starlark-go/blob/master/doc/spec.md#string-interpolation
 func interpolate(format string, x Value) (Value, error) {
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	index := 0
 	nargs := 1
 	if tuple, ok := x.(Tuple); ok {
@@ -1367,7 +1366,7 @@ func interpolate(format string, x Value) (Value, error) {
 			if str, ok := AsString(arg); ok && c == 's' {
 				buf.WriteString(str)
 			} else {
-				writeValue(&buf, arg, nil)
+				writeValue(buf, arg, nil)
 			}
 		case 'd', 'i', 'o', 'x', 'X':
 			i, err := NumberToInt(arg)
@@ -1376,13 +1375,13 @@ func interpolate(format string, x Value) (Value, error) {
 			}
 			switch c {
 			case 'd', 'i':
-				fmt.Fprintf(&buf, "%d", i)
+				fmt.Fprintf(buf, "%d", i)
 			case 'o':
-				fmt.Fprintf(&buf, "%o", i)
+				fmt.Fprintf(buf, "%o", i)
 			case 'x':
-				fmt.Fprintf(&buf, "%x", i)
+				fmt.Fprintf(buf, "%x", i)
 			case 'X':
-				fmt.Fprintf(&buf, "%X", i)
+				fmt.Fprintf(buf, "%X", i)
 			}
 		case 'e', 'f', 'g', 'E', 'F', 'G':
 			f, ok := AsFloat(arg)
@@ -1391,17 +1390,17 @@ func interpolate(format string, x Value) (Value, error) {
 			}
 			switch c {
 			case 'e':
-				fmt.Fprintf(&buf, "%e", f)
+				fmt.Fprintf(buf, "%e", f)
 			case 'f':
-				fmt.Fprintf(&buf, "%f", f)
+				fmt.Fprintf(buf, "%f", f)
 			case 'g':
-				fmt.Fprintf(&buf, "%g", f)
+				fmt.Fprintf(buf, "%g", f)
 			case 'E':
-				fmt.Fprintf(&buf, "%E", f)
+				fmt.Fprintf(buf, "%E", f)
 			case 'F':
-				fmt.Fprintf(&buf, "%F", f)
+				fmt.Fprintf(buf, "%F", f)
 			case 'G':
-				fmt.Fprintf(&buf, "%G", f)
+				fmt.Fprintf(buf, "%G", f)
 			}
 		case 'c':
 			switch arg := arg.(type) {
diff --git a/starlark/library.go b/starlark/library.go
index 5b7faad..7f5444d 100644
--- a/starlark/library.go
+++ b/starlark/library.go
@@ -10,7 +10,6 @@ package starlark
 // mutable types such as lists and dicts.
 
 import (
-	"bytes"
 	"fmt"
 	"log"
 	"math/big"
@@ -837,7 +836,7 @@ func print(thread *Thread, fn *Builtin, args Tuple, kwargs []Tuple) (Value, erro
 	if err := UnpackArgs("print", nil, kwargs, "sep?", &sep); err != nil {
 		return nil, err
 	}
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	for i, v := range args {
 		if i > 0 {
 			buf.WriteString(sep)
@@ -845,14 +844,15 @@ func print(thread *Thread, fn *Builtin, args Tuple, kwargs []Tuple) (Value, erro
 		if s, ok := AsString(v); ok {
 			buf.WriteString(s)
 		} else {
-			writeValue(&buf, v, nil)
+			writeValue(buf, v, nil)
 		}
 	}
 
+	s := buf.String()
 	if thread.Print != nil {
-		thread.Print(thread, buf.String())
+		thread.Print(thread, s)
 	} else {
-		fmt.Fprintln(os.Stderr, &buf)
+		fmt.Fprintln(os.Stderr, s)
 	}
 	return None, nil
 }
@@ -1474,7 +1474,7 @@ func string_capitalize(fnname string, recv Value, args Tuple, kwargs []Tuple) (V
 		return nil, err
 	}
 	s := string(recv.(String))
-	var res bytes.Buffer
+	res := new(strings.Builder)
 	res.Grow(len(s))
 	for i, r := range s {
 		if i == 0 {
@@ -1657,7 +1657,7 @@ func string_find(fnname string, recv Value, args Tuple, kwargs []Tuple) (Value,
 func string_format(fnname string, recv_ Value, args Tuple, kwargs []Tuple) (Value, error) {
 	format := string(recv_.(String))
 	var auto, manual bool // kinds of positional indexing used
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	index := 0
 	for {
 		literal := format
@@ -1782,10 +1782,10 @@ func string_format(fnname string, recv_ Value, args Tuple, kwargs []Tuple) (Valu
 			if str, ok := AsString(arg); ok {
 				buf.WriteString(str)
 			} else {
-				writeValue(&buf, arg, nil)
+				writeValue(buf, arg, nil)
 			}
 		case "r":
-			writeValue(&buf, arg, nil)
+			writeValue(buf, arg, nil)
 		default:
 			return nil, fmt.Errorf("unknown conversion %q", conv)
 		}
@@ -1823,7 +1823,7 @@ func string_join(fnname string, recv_ Value, args Tuple, kwargs []Tuple) (Value,
 	}
 	iter := iterable.Iterate()
 	defer iter.Done()
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	var x Value
 	for i := 0; iter.Next(&x); i++ {
 		if i > 0 {
@@ -1984,7 +1984,7 @@ func string_title(fnname string, recv Value, args Tuple, kwargs []Tuple) (Value,
 	// Python semantics differ from x==strings.{To,}Title(x) in Go:
 	// "uppercase characters may only follow uncased characters and
 	// lowercase characters only cased ones."
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	buf.Grow(len(s))
 	var prevCased bool
 	for _, r := range s {
diff --git a/starlark/value.go b/starlark/value.go
index f697442..116c8e9 100644
--- a/starlark/value.go
+++ b/starlark/value.go
@@ -67,7 +67,6 @@ package starlark // import "go.starlark.net/starlark"
 // This file defines the data types of Starlark and their basic operations.
 
 import (
-	"bytes"
 	"fmt"
 	"math"
 	"math/big"
@@ -980,8 +979,8 @@ func (s *Set) Union(iter Iterator) (Value, error) {
 // toString returns the string form of value v.
 // It may be more efficient than v.String() for larger values.
 func toString(v Value) string {
-	var buf bytes.Buffer
-	writeValue(&buf, v, nil)
+	buf := new(strings.Builder)
+	writeValue(buf, v, nil)
 	return buf.String()
 }
 
@@ -992,7 +991,7 @@ func toString(v Value) string {
 // (These are the only potentially cyclic structures.)
 // Callers should generally pass a temporary slice of length zero but non-zero capacity.
 // It is safe to re-use the same path slice for multiple calls.
-func writeValue(out *bytes.Buffer, x Value, path []Value) {
+func writeValue(out *strings.Builder, x Value, path []Value) {
 	switch x := x.(type) {
 	case nil:
 		out.WriteString("<nil>") // indicates a bug
diff --git a/starlarkstruct/struct.go b/starlarkstruct/struct.go
index ac9c955..1982cc0 100644
--- a/starlarkstruct/struct.go
+++ b/starlarkstruct/struct.go
@@ -23,9 +23,9 @@ package starlarkstruct // import "go.starlark.net/starlarkstruct"
 //    would be, and, like the Go struct, requires only a single allocation.
 
 import (
-	"bytes"
 	"fmt"
 	"sort"
+	"strings"
 
 	"go.starlark.net/starlark"
 	"go.starlark.net/syntax"
@@ -131,7 +131,7 @@ func (s *Struct) ToStringDict(d starlark.StringDict) {
 }
 
 func (s *Struct) String() string {
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	if s.constructor == Default {
 		// NB: The Java implementation always prints struct
 		// even for Bazel provider instances.
diff --git a/starlarktest/starlarktest.go b/starlarktest/starlarktest.go
index 5436d22..c93eaf9 100644
--- a/starlarktest/starlarktest.go
+++ b/starlarktest/starlarktest.go
@@ -13,11 +13,11 @@
 package starlarktest // import "go.starlark.net/starlarktest"
 
 import (
-	"bytes"
 	"fmt"
 	"go/build"
 	"path/filepath"
 	"regexp"
+	"strings"
 	"sync"
 
 	"go.starlark.net/starlark"
@@ -104,8 +104,8 @@ func error_(thread *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, k
 	if len(args) != 1 {
 		return nil, fmt.Errorf("error: got %d arguments, want 1", len(args))
 	}
-	var buf bytes.Buffer
-	thread.Caller().WriteBacktrace(&buf)
+	buf := new(strings.Builder)
+	thread.Caller().WriteBacktrace(buf)
 	buf.WriteString("Error: ")
 	if s, ok := starlark.AsString(args[0]); ok {
 		buf.WriteString(s)
diff --git a/syntax/quote.go b/syntax/quote.go
index d31eb2a..cc9a8d0 100644
--- a/syntax/quote.go
+++ b/syntax/quote.go
@@ -7,7 +7,6 @@ package syntax
 // Starlark quoted string utilities.
 
 import (
-	"bytes"
 	"fmt"
 	"strconv"
 	"strings"
@@ -95,7 +94,7 @@ func unquote(quoted string) (s string, triple bool, err error) {
 	// Otherwise process quoted string.
 	// Each iteration processes one escape sequence along with the
 	// plain text leading up to it.
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	for {
 		// Remove prefix before escape sequence.
 		i := strings.IndexAny(quoted, unquoteChars)
@@ -204,7 +203,7 @@ func quote(unquoted string, triple bool) string {
 		q = `"""`
 	}
 
-	var buf bytes.Buffer
+	buf := new(strings.Builder)
 	buf.WriteString(q)
 
 	for i := 0; i < len(unquoted); i++ {
diff --git a/syntax/scan.go b/syntax/scan.go
index 7fbc5d6..5b3fcbc 100644
--- a/syntax/scan.go
+++ b/syntax/scan.go
@@ -7,7 +7,6 @@ package syntax
 // A lexical scanner for Starlark.
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -832,7 +831,7 @@ func (sc *scanner) scanString(val *tokenValue, quote rune) Token {
 		// A triple-quoted string literal may span multiple
 		// gulps of REPL input; it is the only such token.
 		// Thus we must avoid {start,end}Token.
-		var raw bytes.Buffer
+		raw := new(strings.Builder)
 
 		// Copy the prefix, e.g. r''' or """ (see startToken).
 		raw.Write(sc.token[:len(sc.token)-len(sc.rest)])