template

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 Go to latest Published: Aug 26, 2011 License: BSD-3-Clause Imports: 13 Imported by: 0

Documentation

Overview

Package template implements data-driven templates for generating textual output such as HTML.

Templates are executed by applying them to a data structure. Annotations in the template refer to elements of the data structure (typically a field of a struct or a key in a map) to control execution and derive values to be displayed. Execution of the template walks the structure and sets the cursor, represented by a period '.' and called "dot", to the value at the current location in the structure as execution proceeds.

The input text for a template is UTF-8-encoded text in any format. "Actions"--data evaluations or control structures--are delimited by "{{" and "}}"; all text outside actions is copied to the output unchanged. Actions may not span newlines, although comments can.

Once constructed, templates and template sets can be executed safely in parallel.

Actions

Here is the list of actions. "Arguments" and "pipelines" are evaluations of data, defined in detail below. 

{{/* a comment */}}
	A comment; discarded. May contain newlines.
	Comments do not nest.

{{pipeline}}
	The default textual representation of the value of the pipeline
	is copied to the output.

{{if pipeline}} T1 {{end}}
	If the value of the pipeline is empty, no output is generated;
	otherwise, T1 is executed.  The empty values are false, 0, any
	nil pointer or interface value, and any array, slice, map, or
	string of length zero.
	Dot is unaffected.

{{if pipeline}} T1 {{else}} T0 {{end}}
	If the value of the pipeline is empty, T0 is executed;
	otherwise, T1 is executed.  Dot is unaffected.

{{range pipeline}} T1 {{end}}
	The value of the pipeline must be an array, slice, or map. If
	the value of the pipeline has length zero, nothing is output;
	otherwise, dot is set to the successive elements of the array,
	slice, or map and T1 is executed.

{{range pipeline}} T1 {{else}} T0 {{end}}
	The value of the pipeline must be an array, slice, or map. If
	the value of the pipeline has length zero, dot is unaffected and
	T0 is executed; otherwise, dot is set to the successive elements
	of the array, slice, or map and T1 is executed.

{{template "name"}}
	The template with the specified name is executed with nil data.

{{template "name" pipeline}}
	The template with the specified name is executed with dot set
	to the value of the pipeline.

{{with pipeline}} T1 {{end}}
	If the value of the pipeline is empty, no output is generated;
	otherwise, dot is set to the value of the pipeline and T1 is
	executed.

{{with pipeline}} T1 {{else}} T0 {{end}}
	If the value of the pipeline is empty, dot is unaffected and T0
	is executed; otherwise, dot is set to the value of the pipeline
	and T1 is executed.

Arguments

An argument is a simple value, denoted by one of the following.

  • A boolean, string, character, integer, floating-point, imaginary or complex constant in Go syntax. These behave like Go's untyped constants, although raw strings may not span newlines.
  • The character '.' (period): . The result is the value of dot.
  • A variable name, which is a (possibly empty) alphanumeric string preceded by a dollar sign, such as $piOver2 or $ The result is the value of the variable. Variables are described below.
  • The name of a field of the data, which must be a struct, preceded by a period, such as .Field The result is the value of the field. Field invocations may be chained: .Field1.Field2 Fields can also be evaluated on variables, including chaining: $x.Field1.Field2
  • The name of a key of the data, which must be a map, preceded by a period, such as .Key The result is the map element value indexed by the key. Key invocations may be chained and combined with fields to any depth: .Field1.Key1.Field2.Key2 Although the key must be an alphanumeric identifier, unlike with field names they do not need to start with an upper case letter. Keys can also be evaluated on variables, including chaining: $x.key1.key2
  • The name of a niladic method of the data, preceded by a period, such as .Method The result is the value of invoking the method with dot as the receiver, dot.Method(). Such a method must have one return value (of any type) or two return values, the second of which is an os.Error. If it has two and the returned error is non-nil, execution terminates and an error is returned to the caller as the value of Execute. Method invocations may be chained and combined with fields and keys to any depth: .Field1.Key1.Method1.Field2.Key2.Method2 Methods can also be evaluated on variables, including chaining: $x.Method1.Field
  • The name of a niladic function, such as fun The result is the value of invoking the function, fun(). The return types and values behave as in methods. Functions and function names are described below.

Arguments may evaluate to any type; if they are pointers the implementation automatically indirects to the base type when required.

A pipeline is a possibly chained sequence of "commands". A command is a simple value (argument) or a function or method call, possibly with multiple arguments: 

Argument
	The result is the value of evaluating the argument.
.Method [Argument...]
	The method can be alone or the last element of a chain but,
	unlike methods in the middle of a chain, it can take arguments.
	The result is the value of calling the method with the
	arguments:
		dot.Method(Argument1, etc.)
functionName [Argument...]
	The result is the value of calling the function associated
	with the name:
		function(Argument1, etc.)
	Functions and function names are described below.

Pipelines

A pipeline may be "chained" by separating a sequence of commands with pipeline characters '|'. In a chained pipeline, the result of the each command is passed as the last argument of the following command. The output of the final command in the pipeline is the value of the pipeline.

The output of a command will be either one value or two values, the second of which has type os.Error. If that second value is present and evaluates to non-nil, execution terminates and the error is returned to the caller of Execute.

Variables

A pipeline inside an action may initialize a variable to capture the result. The initialization has syntax 

$variable := pipeline

where $variable is the name of the variable. An action that declares a variable produces no output.

If a "range" action initializes a variable, the variable is set to the successive elements of the iteration. Also, a "range" may declare two variables, separated by a comma: 

$index, $element := pipeline

in which case $index and $element are set to the successive values of the array/slice index or map key and element, respectively. Note that if there is only one variable, it is assigned the element; this is opposite to the convention in Go range clauses.

A variable's scope extends to the "end" action of the control structure ("if", "with", or "range") in which it is declared, or to the end of the template if there is no such control structure. A template invocation does not inherit variables from the point of its invocation.

When execution begins, $ is set to the data argument passed to Execute, that is, to the starting value of dot.

Examples

Here are some example one-line templates demonstrating pipelines and variables. All produce the quoted word "output": 

{{"\"output\""}}
	A string constant.
{{`"output"`}}
	A raw string constant.
{{printf "%q" "output"}}
	A function call.
{{"output" | printf "%q"}}
	A function call whose final argument comes from the previous
	command.
{{"put" | printf "%s%s" "out" | printf "%q"}}
	A more elaborate call.
{{"output" | printf "%s" | printf "%q"}}
	A longer chain.
{{with "output"}}{{printf "%q" .}}{{end}}
	A with action using dot.
{{with $x := "output" | printf "%q"}}{{$x}}{{end}}
	A with action that creates and uses a variable.
{{with $x := "output"}}{{printf "%q" $x}}{{end}}
	A with action that uses the variable in another action.
{{with $x := "output"}}{{$x | printf "%q"}}{{end}}
	The same, but pipelined.

Functions

During execution functions are found in three function maps: first in the template, then in the "template set" (described below), and finally in the global function map. By default, no functions are defined in the template or the set but the Funcs methods can be used to add them.

Predefined global functions are named as follows. 

and
	Returns the boolean AND of its arguments by returning the
	first empty argument or the last argument, that is,
	"and x y" behaves as "if x then y else x". All the
	arguments are evaluated.
html
	Returns the escaped HTML equivalent of the textual
	representation of its arguments.
index
	Returns the result of indexing its first argument by the
	following arguments. Thus "index x 1 2 3" is, in Go syntax,
	x[1][2][3]. Each indexed item must be a map, slice, or array.
js
	Returns the escaped JavaScript equivalent of the textual
	representation of its arguments.
len
	Returns the integer length of its argument.
not
	Returns the boolean negation of its single argument.
or
	Returns the boolean OR of its arguments by returning the
	first non-empty argument or the last argument, that is,
	"or x y" behaves as "if x then x else y". All the
	arguments are evaluated.
print
	An alias for fmt.Sprint
printf
	An alias for fmt.Sprintf
println
	An alias for fmt.Sprintln
urlquery
	Returns the escaped value of the textual representation of
	its arguments in a form suitable for embedding in a URL query.

The boolean functions take any zero value to be false and a non-zero value to be true.

Template sets

Each template is named by a string specified when it is created. A template may use a template invocation to instantiate another template directly or by its name; see the explanation of the template action above. The name is looked up in the template set associated with the template.

If no template invocation actions occur in the template, the issue of template sets can be ignored. If it does contain invocations, though, the template containing the invocations must be part of a template set in which to look up the names.

There are two ways to construct template sets.

The first is to use a Set's Parse method to create a set of named templates from a single input defining multiple templates. The syntax of the definitions is to surround each template declaration with a define and end action.

The define action names the template being created by providing a string constant. Here is a simple example of input to Set.Parse: 

`{{define "T1"}} definition of template T1 {{end}}
{{define "T2"}} definition of template T2 {{end}}
{{define "T3"}} {{template "T1"}} {{template "T2"}} {{end}}`

This defines two templates, T1 and T2, and a third T3 that invokes the other two when it is executed.

The second way to build a template set is to use Set's Add method to add a parsed template to a set. A template may be bound to at most one set. If it's necessary to have a template in multiple sets, the template definition must be parsed multiple times to create distinct *Template values.

Set.Parse may be called multiple times on different inputs to construct the set. Two sets may therefore be constructed with a common base set of templates plus, through a second Parse call each, specializations for some elements.

A template may be executed directly or through Set.Execute, which executes a named template from the set. To invoke our example above, we might write, 

err := set.Execute(os.Stdout, "T3", "no data needed")
if err != nil {
	log.Fatalf("execution failed: %s", err)
}

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func HTMLEscape 

func HTMLEscape(w io.Writer, b []byte)

HTMLEscape writes to w the escaped HTML equivalent of the plain text data b.

func HTMLEscapeString 

func HTMLEscapeString(s string) string

HTMLEscapeString returns the escaped HTML equivalent of the plain text data s.

func HTMLEscaper 

func HTMLEscaper(args ...interface{}) string

HTMLEscaper returns the escaped HTML equivalent of the textual representation of its arguments.

func JSEscape 

func JSEscape(w io.Writer, b []byte)

JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.

func JSEscapeString 

func JSEscapeString(s string) string

JSEscapeString returns the escaped JavaScript equivalent of the plain text data s.

func JSEscaper 

func JSEscaper(args ...interface{}) string

JSEscaper returns the escaped JavaScript equivalent of the textual representation of its arguments.

func URLQueryEscaper 

func URLQueryEscaper(args ...interface{}) string

URLQueryEscaper returns the escaped value of the textual representation of its arguments in a form suitable for embedding in a URL query.

Types

type FuncMap 

type FuncMap map[string]interface{}

FuncMap is the type of the map defining the mapping from names to functions. Each function must have either a single return value, or two return values of which the second has type os.Error. If the second argument evaluates to non-nil during execution, execution terminates and Execute returns an error.

type Set 

type Set struct {
	// contains filtered or unexported fields
}

Set holds a set of related templates that can refer to one another by name. The zero value represents an empty set. A template may be a member of multiple sets.

func ParseSetFiles 

func ParseSetFiles(filenames ...string) (*Set, os.Error)

ParseSetFiles creates a new Set and parses the set definition from the named files. Each file must be individually parseable.

func ParseSetGlob 

func ParseSetGlob(pattern string) (*Set, os.Error)

ParseSetGlob creates a new Set and parses the set definition from the files identified by the pattern. The pattern is processed by filepath.Glob and must match at least one file.

func ParseTemplateFiles 

func ParseTemplateFiles(filenames ...string) (*Set, os.Error)

ParseTemplateFiles creates a set by parsing the named files, each of which defines a single template. Each template will be named the base name of its file. Unlike with ParseFiles, each file should be a stand-alone template definition suitable for Template.Parse (not Set.Parse); that is, the file does not contain {{define}} clauses. ParseTemplateFiles is therefore equivalent to calling the ParseFile function to create individual templates, which are then added to the set. Each file must be parseable by itself. Parsing stops if an error is encountered.

func ParseTemplateGlob 

func ParseTemplateGlob(pattern string) (*Set, os.Error)

ParseTemplateGlob creates a set by parsing the files matched by the pattern, each of which defines a single template. Each template will be named the base name of its file. Unlike with ParseGlob, each file should be a stand-alone template definition suitable for Template.Parse (not Set.Parse); that is, the file does not contain {{define}} clauses. ParseTemplateGlob is therefore equivalent to calling the ParseFile function to create individual templates, which are then added to the set. Each file must be parseable by itself. Parsing stops if an error is encountered.

func SetMust 

func SetMust(s *Set, err os.Error) *Set

SetMust is a helper that wraps a call to a function returning (*Set, os.Error) and panics if the error is non-nil. It is intended for use in variable initializations such as 

var s = template.SetMust(template.ParseSetFiles("file"))

func (*Set) Add 

func (s *Set) Add(templates ...*Template) *Set

Add adds the argument templates to the set. It panics if two templates with the same name are added or if a template is already a member of a set. The return value is the set, so calls can be chained.

func (*Set) Execute 

func (s *Set) Execute(wr io.Writer, name string, data interface{}) os.Error

Execute applies the named template to the specified data object, writing the output to wr.

func (*Set) FuncMap 

func (s *Set) FuncMap() FuncMap

FuncMap returns the set's function map.

func (*Set) Funcs 

func (s *Set) Funcs(funcMap FuncMap) *Set

Funcs adds the elements of the argument map to the set's function map. It panics if a value in the map is not a function with appropriate return type. The return value is the set, so calls can be chained.

func (*Set) Parse 

func (s *Set) Parse(text string) (*Set, os.Error)

Parse parses a string into a set of named templates. Parse may be called multiple times for a given set, adding the templates defined in the string to the set. If a template is redefined, the element in the set is overwritten with the new definition.

func (*Set) ParseFiles 

func (s *Set) ParseFiles(filenames ...string) (*Set, os.Error)

ParseFiles parses the named files into a set of named templates. Each file must be parseable by itself. If an error occurs, parsing stops and the returned set is nil.

func (*Set) ParseGlob 

func (s *Set) ParseGlob(pattern string) (*Set, os.Error)

ParseGlob parses the set definition from the files identified by the pattern. The pattern is processed by filepath.Glob and must match at least one file. If an error occurs, parsing stops and the returned set is nil.

func (*Set) ParseTemplateFiles 

func (s *Set) ParseTemplateFiles(filenames ...string) (*Set, os.Error)

ParseTemplateFiles parses the named template files and adds them to the set. Each template will be named the base name of its file. Unlike with ParseFiles, each file should be a stand-alone template definition suitable for Template.Parse (not Set.Parse); that is, the file does not contain {{define}} clauses. ParseTemplateFiles is therefore equivalent to calling the ParseFile function to create individual templates, which are then added to the set. Each file must be parseable by itself. If an error occurs, parsing stops and the returned set is nil.

func (*Set) ParseTemplateGlob 

func (s *Set) ParseTemplateGlob(pattern string) (*Set, os.Error)

ParseTemplateGlob parses the template files matched by the patern and adds them to the set. Each template will be named the base name of its file. Unlike with ParseGlob, each file should be a stand-alone template definition suitable for Template.Parse (not Set.Parse); that is, the file does not contain {{define}} clauses. ParseTemplateGlob is therefore equivalent to calling the ParseFile function to create individual templates, which are then added to the set. Each file must be parseable by itself. If an error occurs, parsing stops and the returned set is nil.

func (*Set) Template 

func (s *Set) Template(name string) *Template

Template returns the template with the given name in the set, or nil if there is no such template.

type Template 

type Template struct {
	*parse.Tree
	// contains filtered or unexported fields
}

Template is the representation of a parsed template.

func Must 

func Must(t *Template, err os.Error) *Template

Must is a helper that wraps a call to a function returning (*Template, os.Error) and panics if the error is non-nil. It is intended for use in variable initializations such as 

var t = template.Must(template.New("name").Parse("text"))

func New 

func New(name string) *Template

New allocates a new template with the given name.

func ParseFile 

func ParseFile(filename string) (*Template, os.Error)

ParseFile creates a new Template and parses the template definition from the named file. The template name is the base name of the file.

func (*Template) Execute 

func (t *Template) Execute(wr io.Writer, data interface{}) (err os.Error)

Execute applies a parsed template to the specified data object, writing the output to wr.

func (*Template) Funcs 

func (t *Template) Funcs(funcMap FuncMap) *Template

Funcs adds the elements of the argument map to the template's function map. It panics if a value in the map is not a function with appropriate return type. The return value is the template, so calls can be chained.

func (*Template) Name 

func (t *Template) Name() string

Name returns the name of the template.

func (*Template) Parse 

func (t *Template) Parse(s string) (tmpl *Template, err os.Error)

Parse parses the template definition string to construct an internal representation of the template for execution.

func (*Template) ParseFile 

func (t *Template) ParseFile(filename string) (*Template, os.Error)

ParseFile reads the template definition from a file and parses it to construct an internal representation of the template for execution. The returned template will be nil if an error occurs.

func (*Template) ParseInSet 

func (t *Template) ParseInSet(s string, set *Set) (tmpl *Template, err os.Error)

ParseInSet parses the template definition string to construct an internal representation of the template for execution. It also adds the template to the set. Function bindings are checked against those in the set.

Source Files

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Directories

Path Synopsis
Package parse builds parse trees for templates.
 Package parse builds parse trees for templates.

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