Source file src/pkg/internal/lazytemplate/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 interface{}) 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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