go option 源码
golang option 代码
文件路径：/src/text/template/option.go
// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file contains the code to handle template options.
package template
import "strings"
// missingKeyAction defines how to respond to indexing a map with a key that is not present.
type missingKeyAction int
const (
mapInvalid missingKeyAction = iota // Return an invalid reflect.Value.
mapZeroValue // Return the zero value for the map element.
mapError // Error out
)
type option struct {
missingKey missingKeyAction
}
// Option sets options for the template. Options are described by
// strings, either a simple string or "key=value". There can be at
// most one equals sign in an option string. If the option string
// is unrecognized or otherwise invalid, Option panics.
//
// Known options:
//
// missingkey: Control the behavior during execution if a map is
// indexed with a key that is not present in the map.
//
// "missingkey=default" or "missingkey=invalid"
// The default behavior: Do nothing and continue execution.
// If printed, the result of the index operation is the string
// "<no value>".
// "missingkey=zero"
// The operation returns the zero value for the map type's element.
// "missingkey=error"
// Execution stops immediately with an error.
func (t *Template) Option(opt ...string) *Template {
t.init()
for _, s := range opt {
t.setOption(s)
}
return t
}
func (t *Template) setOption(opt string) {
if opt == "" {
panic("empty option string")
}
// key=value
if key, value, ok := strings.Cut(opt, "="); ok {
switch key {
case "missingkey":
switch value {
case "invalid", "default":
t.option.missingKey = mapInvalid
return
case "zero":
t.option.missingKey = mapZeroValue
return
case "error":
t.option.missingKey = mapError
return
}
}
}
panic("unrecognized option: " + opt)
}
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