option.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // This file contains the code to handle template options.
     6  
     7  package template
     8  
     9  import "strings"
    10  
    11  // missingKeyAction defines how to respond to indexing a map with a key that is not present.
    12  type missingKeyAction int
    13  
    14  const (
    15  	mapInvalid   missingKeyAction = iota // Return an invalid reflect.Value.
    16  	mapZeroValue                         // Return the zero value for the map element.
    17  	mapError                             // Error out
    18  )
    19  
    20  type option struct {
    21  	missingKey missingKeyAction
    22  }
    23  
    24  // Option sets options for the template. Options are described by
    25  // strings, either a simple string or "key=value". There can be at
    26  // most one equals sign in an option string. If the option string
    27  // is unrecognized or otherwise invalid, Option panics.
    28  //
    29  // Known options:
    30  //
    31  // missingkey: Control the behavior during execution if a map is
    32  // indexed with a key that is not present in the map.
    33  //
    34  //	"missingkey=default" or "missingkey=invalid"
    35  //		The default behavior: Do nothing and continue execution.
    36  //		If printed, the result of the index operation is the string
    37  //		"<no value>".
    38  //	"missingkey=zero"
    39  //		The operation returns the zero value for the map type's element.
    40  //	"missingkey=error"
    41  //		Execution stops immediately with an error.
    42  func (t *Template) Option(opt ...string) *Template {
    43  	t.init()
    44  	for _, s := range opt {
    45  		t.setOption(s)
    46  	}
    47  	return t
    48  }
    49  
    50  func (t *Template) setOption(opt string) {
    51  	if opt == "" {
    52  		panic("empty option string")
    53  	}
    54  	// key=value
    55  	if key, value, ok := strings.Cut(opt, "="); ok {
    56  		switch key {
    57  		case "missingkey":
    58  			switch value {
    59  			case "invalid", "default":
    60  				t.option.missingKey = mapInvalid
    61  				return
    62  			case "zero":
    63  				t.option.missingKey = mapZeroValue
    64  				return
    65  			case "error":
    66  				t.option.missingKey = mapError
    67  				return
    68  			}
    69  		}
    70  	}
    71  	panic("unrecognized option: " + opt)
    72  }
    73
View as plain text