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Source file src/text/template/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	//	"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		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		elems := strings.Split(opt, "=")
    55		switch len(elems) {
    56		case 2:
    57			// key=value
    58			switch elems[0] {
    59			case "missingkey":
    60				switch elems[1] {
    61				case "invalid", "default":
    62					t.option.missingKey = mapInvalid
    63					return
    64				case "zero":
    65					t.option.missingKey = mapZeroValue
    66					return
    67				case "error":
    68					t.option.missingKey = mapError
    69					return
    70				}
    71			}
    72		}
    73		panic("unrecognized option: " + opt)
    74	}
    75	

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