diff options
Diffstat (limited to 'src/lib/fmt/print.go')
| -rw-r--r-- | src/lib/fmt/print.go | 62 |
1 files changed, 51 insertions, 11 deletions
diff --git a/src/lib/fmt/print.go b/src/lib/fmt/print.go index 99dfe7614..b5b1fed45 100644 --- a/src/lib/fmt/print.go +++ b/src/lib/fmt/print.go @@ -2,12 +2,21 @@ // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. +// Package fmt implements formatted I/O with functions analogous +// to C's printf. Because of reflection knowledge it does not need +// to be told about sizes and signedness (no %llud etc. - just %d). +// Still to do: document the formats properly. For now, like C but: +// - don't need l or u flags - type of integer tells that. +// - %v prints any value using its native format. +// - for each Printf-like fn, there is also a Print fn that takes no format +// and is equivalent to saying %v for every operand. +// - another variant Println inserts blanks and appends a newline. +// - if an operand implements method String() that method will +// be used for %v, %s, or Print etc. +// - if an operand implements interface Formatter, that interface can +// be used for fine control of formatting. package fmt -/* - C-like printf, but because of reflection knowledge does not need - to be told about sizes and signedness (no %llud etc. - just %d). -*/ import ( "fmt"; @@ -17,27 +26,37 @@ import ( "utf8"; ) -// Representation of printer state passed to custom formatters. -// Provides access to the io.Write interface plus information about -// the active formatting verb. +// Formatter represents the printer state passed to custom formatters. +// It provides access to the io.Write interface plus information about +// the flags and options for the operand's format specifier. type Formatter interface { + // Write is the function to call to emit formatted output to be printed. Write(b []byte) (ret int, err *os.Error); + // Width returns the value of the width option and whether it has been set. Width() (wid int, ok bool); + // Precision returns the value of the precision option and whether it has been set. Precision() (prec int, ok bool); - // flags + // Flag returns whether the flag c, a character, has been set. Flag(int) bool; } +// Format is the interface implemented by objects with a custom formatter. +// The implementation of Format may call Sprintf or Fprintf(f) etc. +// to generate its output. type Format interface { Format(f Formatter, c int); } +// String represents any object being printed that has a String() method that +// returns a string, which defines the ``native'' format for that object. +// Any such object will be printed using that method if passed +// as operand to a %s or %v format or to an unformatted printer such as Print. type String interface { String() string } -const runeSelf = 0x80 +const runeSelf = utf8.RuneSelf const allocSize = 32 type pp struct { @@ -129,6 +148,7 @@ func (p *pp) doprint(v reflect.StructValue, addspace, addnewline bool); // These routines end in 'f' and take a format string. +// Fprintf formats according to a format specifier and writes to w. func Fprintf(w io.Write, format string, a ...) (n int, error *os.Error) { v := reflect.NewValue(a).(reflect.StructValue); p := newPrinter(); @@ -137,11 +157,13 @@ func Fprintf(w io.Write, format string, a ...) (n int, error *os.Error) { return n, error; } +// Printf formats according to a format specifier and writes to standard output. func Printf(format string, v ...) (n int, errno *os.Error) { n, errno = Fprintf(os.Stdout, format, v); return n, errno; } +// Sprintf formats according to a format specifier and returns the resulting string. func Sprintf(format string, a ...) string { v := reflect.NewValue(a).(reflect.StructValue); p := newPrinter(); @@ -150,9 +172,10 @@ func Sprintf(format string, a ...) string { return s; } -// These routines do not take a format string and add spaces only -// when the operand on neither side is a string. +// These routines do not take a format string +// Fprint formats using the default formats for its operands and writes to w. +// Spaces are added between operands when neither is a string. func Fprint(w io.Write, a ...) (n int, error *os.Error) { v := reflect.NewValue(a).(reflect.StructValue); p := newPrinter(); @@ -161,11 +184,15 @@ func Fprint(w io.Write, a ...) (n int, error *os.Error) { return n, error; } +// Print formats using the default formats for its operands and writes to standard output. +// Spaces are added between operands when neither is a string. func Print(v ...) (n int, errno *os.Error) { n, errno = Fprint(os.Stdout, v); return n, errno; } +// Sprint formats using the default formats for its operands and returns the resulting string. +// Spaces are added between operands when neither is a string. func Sprint(a ...) string { v := reflect.NewValue(a).(reflect.StructValue); p := newPrinter(); @@ -178,6 +205,8 @@ func Sprint(a ...) string { // always add spaces between operands, and add a newline // after the last operand. +// Fprintln formats using the default formats for its operands and writes to w. +// Spaces are always added between operands and a newline is appended. func Fprintln(w io.Write, a ...) (n int, error *os.Error) { v := reflect.NewValue(a).(reflect.StructValue); p := newPrinter(); @@ -186,11 +215,15 @@ func Fprintln(w io.Write, a ...) (n int, error *os.Error) { return n, error; } +// Println formats using the default formats for its operands and writes to standard output. +// Spaces are always added between operands and a newline is appended. func Println(v ...) (n int, errno *os.Error) { n, errno = Fprintln(os.Stdout, v); return n, errno; } +// Sprintln formats using the default formats for its operands and returns the resulting string. +// Spaces are always added between operands and a newline is appended. func Sprintln(a ...) string { v := reflect.NewValue(a).(reflect.StructValue); p := newPrinter(); @@ -596,6 +629,13 @@ func (p *pp) doprintf(format string, v reflect.StructValue) { // string case 's': + if inter != nil { + // if object implements String, use the result. + if stringer, ok := inter.(String); ok { + s = p.fmt.Fmt_s(stringer.String()).Str(); + break; + } + } if v, ok := getString(field); ok { s = p.fmt.Fmt_s(v).Str() } else { |