lazytemplate.go

     1  // Copyright 2019 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 lazytemplate is a thin wrapper over text/template, allowing the use
     6  // of global template variables without forcing them to be parsed at init.
     7  package lazytemplate
     8  
     9  import (
    10  	"io"
    11  	"os"
    12  	"strings"
    13  	"sync"
    14  	"text/template"
    15  )
    16  
    17  // Template is a wrapper around text/template.Template, where the underlying
    18  // template will be parsed the first time it is needed.
    19  type Template struct {
    20  	name, text string
    21  
    22  	once sync.Once
    23  	tmpl *template.Template
    24  }
    25  
    26  func (r *Template) tp() *template.Template {
    27  	r.once.Do(r.build)
    28  	return r.tmpl
    29  }
    30  
    31  func (r *Template) build() {
    32  	r.tmpl = template.Must(template.New(r.name).Parse(r.text))
    33  	r.name, r.text = "", ""
    34  }
    35  
    36  func (r *Template) Execute(w io.Writer, data any) error {
    37  	return r.tp().Execute(w, data)
    38  }
    39  
    40  var inTest = len(os.Args) > 0 && strings.HasSuffix(strings.TrimSuffix(os.Args[0], ".exe"), ".test")
    41  
    42  // New creates a new lazy template, delaying the parsing work until it is first
    43  // needed. If the code is being run as part of tests, the template parsing will
    44  // happen immediately.
    45  func New(name, text string) *Template {
    46  	lt := &Template{name: name, text: text}
    47  	if inTest {
    48  		// In tests, always parse the templates early.
    49  		lt.tp()
    50  	}
    51  	return lt
    52  }
    53
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