rsc.io/go@v0.0.0-20150416155037-e040fd465409/src/text/template/option.go (about)

     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  //	"missingkey=default" or "missingkey=invalid"
    34  //		The default behavior: Do nothing and continue execution.
    35  //		If printed, the result of the index operation is the string
    36  //		"<no value>".
    37  //	"missingkey=zero"
    38  //		The operation returns the zero value for the map type's element.
    39  //	"missingkey=error"
    40  //		Execution stops immediately with an error.
    41  //
    42  func (t *Template) Option(opt ...string) *Template {
    43  	for _, s := range opt {
    44  		t.setOption(s)
    45  	}
    46  	return t
    47  }
    48  
    49  func (t *Template) setOption(opt string) {
    50  	if opt == "" {
    51  		panic("empty option string")
    52  	}
    53  	elems := strings.Split(opt, "=")
    54  	switch len(elems) {
    55  	case 2:
    56  		// key=value
    57  		switch elems[0] {
    58  		case "missingkey":
    59  			switch elems[1] {
    60  			case "invalid", "default":
    61  				t.option.missingKey = mapInvalid
    62  				return
    63  			case "zero":
    64  				t.option.missingKey = mapZeroValue
    65  				return
    66  			case "error":
    67  				t.option.missingKey = mapError
    68  				return
    69  			}
    70  		}
    71  	}
    72  	panic("unrecognized option: " + opt)
    73  }