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Source file src/text/template/examplefiles_test.go

Documentation: text/template

     1  // Copyright 2012 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  package template_test
     6  
     7  import (
     8  	"io"
     9  	"io/ioutil"
    10  	"log"
    11  	"os"
    12  	"path/filepath"
    13  	"text/template"
    14  )
    15  
    16  // templateFile defines the contents of a template to be stored in a file, for testing.
    17  type templateFile struct {
    18  	name     string
    19  	contents string
    20  }
    21  
    22  func createTestDir(files []templateFile) string {
    23  	dir, err := ioutil.TempDir("", "template")
    24  	if err != nil {
    25  		log.Fatal(err)
    26  	}
    27  	for _, file := range files {
    28  		f, err := os.Create(filepath.Join(dir, file.name))
    29  		if err != nil {
    30  			log.Fatal(err)
    31  		}
    32  		defer f.Close()
    33  		_, err = io.WriteString(f, file.contents)
    34  		if err != nil {
    35  			log.Fatal(err)
    36  		}
    37  	}
    38  	return dir
    39  }
    40  
    41  // Here we demonstrate loading a set of templates from a directory.
    42  func ExampleTemplate_glob() {
    43  	// Here we create a temporary directory and populate it with our sample
    44  	// template definition files; usually the template files would already
    45  	// exist in some location known to the program.
    46  	dir := createTestDir([]templateFile{
    47  		// T0.tmpl is a plain template file that just invokes T1.
    48  		{"T0.tmpl", `T0 invokes T1: ({{template "T1"}})`},
    49  		// T1.tmpl defines a template, T1 that invokes T2.
    50  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
    51  		// T2.tmpl defines a template T2.
    52  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
    53  	})
    54  	// Clean up after the test; another quirk of running as an example.
    55  	defer os.RemoveAll(dir)
    56  
    57  	// pattern is the glob pattern used to find all the template files.
    58  	pattern := filepath.Join(dir, "*.tmpl")
    59  
    60  	// Here starts the example proper.
    61  	// T0.tmpl is the first name matched, so it becomes the starting template,
    62  	// the value returned by ParseGlob.
    63  	tmpl := template.Must(template.ParseGlob(pattern))
    64  
    65  	err := tmpl.Execute(os.Stdout, nil)
    66  	if err != nil {
    67  		log.Fatalf("template execution: %s", err)
    68  	}
    69  	// Output:
    70  	// T0 invokes T1: (T1 invokes T2: (This is T2))
    71  }
    72  
    73  // This example demonstrates one way to share some templates
    74  // and use them in different contexts. In this variant we add multiple driver
    75  // templates by hand to an existing bundle of templates.
    76  func ExampleTemplate_helpers() {
    77  	// Here we create a temporary directory and populate it with our sample
    78  	// template definition files; usually the template files would already
    79  	// exist in some location known to the program.
    80  	dir := createTestDir([]templateFile{
    81  		// T1.tmpl defines a template, T1 that invokes T2.
    82  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
    83  		// T2.tmpl defines a template T2.
    84  		{"T2.tmpl", `{{define "T2"}}This is T2{{end}}`},
    85  	})
    86  	// Clean up after the test; another quirk of running as an example.
    87  	defer os.RemoveAll(dir)
    88  
    89  	// pattern is the glob pattern used to find all the template files.
    90  	pattern := filepath.Join(dir, "*.tmpl")
    91  
    92  	// Here starts the example proper.
    93  	// Load the helpers.
    94  	templates := template.Must(template.ParseGlob(pattern))
    95  	// Add one driver template to the bunch; we do this with an explicit template definition.
    96  	_, err := templates.Parse("{{define `driver1`}}Driver 1 calls T1: ({{template `T1`}})\n{{end}}")
    97  	if err != nil {
    98  		log.Fatal("parsing driver1: ", err)
    99  	}
   100  	// Add another driver template.
   101  	_, err = templates.Parse("{{define `driver2`}}Driver 2 calls T2: ({{template `T2`}})\n{{end}}")
   102  	if err != nil {
   103  		log.Fatal("parsing driver2: ", err)
   104  	}
   105  	// We load all the templates before execution. This package does not require
   106  	// that behavior but html/template's escaping does, so it's a good habit.
   107  	err = templates.ExecuteTemplate(os.Stdout, "driver1", nil)
   108  	if err != nil {
   109  		log.Fatalf("driver1 execution: %s", err)
   110  	}
   111  	err = templates.ExecuteTemplate(os.Stdout, "driver2", nil)
   112  	if err != nil {
   113  		log.Fatalf("driver2 execution: %s", err)
   114  	}
   115  	// Output:
   116  	// Driver 1 calls T1: (T1 invokes T2: (This is T2))
   117  	// Driver 2 calls T2: (This is T2)
   118  }
   119  
   120  // This example demonstrates how to use one group of driver
   121  // templates with distinct sets of helper templates.
   122  func ExampleTemplate_share() {
   123  	// Here we create a temporary directory and populate it with our sample
   124  	// template definition files; usually the template files would already
   125  	// exist in some location known to the program.
   126  	dir := createTestDir([]templateFile{
   127  		// T0.tmpl is a plain template file that just invokes T1.
   128  		{"T0.tmpl", "T0 ({{.}} version) invokes T1: ({{template `T1`}})\n"},
   129  		// T1.tmpl defines a template, T1 that invokes T2. Note T2 is not defined
   130  		{"T1.tmpl", `{{define "T1"}}T1 invokes T2: ({{template "T2"}}){{end}}`},
   131  	})
   132  	// Clean up after the test; another quirk of running as an example.
   133  	defer os.RemoveAll(dir)
   134  
   135  	// pattern is the glob pattern used to find all the template files.
   136  	pattern := filepath.Join(dir, "*.tmpl")
   137  
   138  	// Here starts the example proper.
   139  	// Load the drivers.
   140  	drivers := template.Must(template.ParseGlob(pattern))
   141  
   142  	// We must define an implementation of the T2 template. First we clone
   143  	// the drivers, then add a definition of T2 to the template name space.
   144  
   145  	// 1. Clone the helper set to create a new name space from which to run them.
   146  	first, err := drivers.Clone()
   147  	if err != nil {
   148  		log.Fatal("cloning helpers: ", err)
   149  	}
   150  	// 2. Define T2, version A, and parse it.
   151  	_, err = first.Parse("{{define `T2`}}T2, version A{{end}}")
   152  	if err != nil {
   153  		log.Fatal("parsing T2: ", err)
   154  	}
   155  
   156  	// Now repeat the whole thing, using a different version of T2.
   157  	// 1. Clone the drivers.
   158  	second, err := drivers.Clone()
   159  	if err != nil {
   160  		log.Fatal("cloning drivers: ", err)
   161  	}
   162  	// 2. Define T2, version B, and parse it.
   163  	_, err = second.Parse("{{define `T2`}}T2, version B{{end}}")
   164  	if err != nil {
   165  		log.Fatal("parsing T2: ", err)
   166  	}
   167  
   168  	// Execute the templates in the reverse order to verify the
   169  	// first is unaffected by the second.
   170  	err = second.ExecuteTemplate(os.Stdout, "T0.tmpl", "second")
   171  	if err != nil {
   172  		log.Fatalf("second execution: %s", err)
   173  	}
   174  	err = first.ExecuteTemplate(os.Stdout, "T0.tmpl", "first")
   175  	if err != nil {
   176  		log.Fatalf("first: execution: %s", err)
   177  	}
   178  
   179  	// Output:
   180  	// T0 (second version) invokes T1: (T1 invokes T2: (T2, version B))
   181  	// T0 (first version) invokes T1: (T1 invokes T2: (T2, version A))
   182  }
   183  

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