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Tera Templating Engine

ExTera.Rd

ExTera is an R6 class object that uses extendr to encapsulate Tera's templating engine. In addition to providing rendering functionality, it acts as a library to hold templates that may include complex dependencies, a feature called template "inheritance" in Tera.

Details

A templating engine requires two things:

  • a template, as you may have guessed, that includes variables and rendering logic describing where and how to inject data, and

  • a context, or a set of variables and values to be injected into the template.

Templating syntax is described in the Tera docs.

Methods

Public methods

Method new()

Create a new ExTera object. Will populate template library with files in dir if specified.

Usage

ExTera$new(dir = NULL)

Arguments

dir

character scalar, a glob pattern with * wildcards indicating a potentially nested directory containing multiple file templates. If NULL (the default), an ExTera with an empty library is initialized. See details for more information.

Details

The glob pattern templates/*.html will match all files with the .html extension located directly inside the templates folder, while the glob pattern templates/**/*.html will match all files with the .html extension directly inside or in a subdirectory of templates. The default naming convention is to give each template their full relative path from templates or whatever the directory is called.

Returns

Self (invisibly)

Examples

# initialize ExTera with empty library
tera <- ExTera$new()
tera

# initialize ExTera from directory with glob
template_dir <- file.path(tempdir(), "templates")

dir.create(template_dir)

tmp <- file.path(
  template_dir,
  "hello-world-template.html"
)

writeLines(
  text = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  con = tmp
)

tera <- ExTera$new(dir = file.path(template_dir, "*.html"))
tera

Method print()

print method for ExTera object.

Usage

ExTera$print(n = 10L, ...)

Arguments

n

integer scalar, number of templates to print (default is 10L)

...

ignored

Returns

Self (invisibly)

Method add_file_templates()

Add templates to library from file paths.

Usage

ExTera$add_file_templates(...)

Arguments

...

specify list of templates as key-value pairs where key is the name of the template and value is the path to the template on file.

Details

All templates must be named.

Returns

Self (invisibly)

Examples

tera <- ExTera$new()

writeLines(
  '<p>Hello {{ x }}. This is {{ y }}.</p>',
  con = file.path(tempdir(), "hello-world.html")
)

writeLines(
  '<img src="{{ img_src }}">',
  con = file.path(tempdir(), "img-src.html")
)

tera$add_file_templates(
  "hello-world" = file.path(tempdir(), "hello-world.html"),
  "img-src" = file.path(tempdir(), "img-src.html")
)

tera

Method add_string_templates()

Add templates to library from character strings.

Usage

ExTera$add_string_templates(...)

Arguments

...

specify list of templates as key-value pairs where key is the name of the template and value is a string template.

Details

All templates must be named.

Returns

Self (invisibly)

Examples

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  "img-src" = '<img src="{{ img_src }}">'
)

tera

Method list_templates()

List current templates in library.

Usage

ExTera$list_templates()

Returns

NULL (invisibly)

Examples

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  "img-src" = '<img src="{{ img_src }}">'
)

tera$list_templates()

Method render()

Render specified template to file.

Usage

ExTera$render(template, outfile, ...)

Arguments

template

character scalar, the name of the template to render.

outfile

character scalar, the path to file where template is to be rendered.

...

specify context as key-value pairs where key is the template variable and value is the data to inject.

Details

All context elements must be named.

Returns

outfile (invisibly)

Examples

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

outfile <- file.path(tempdir(), "rendered-hello-world.html")

tera$render(
  "hello-world",
  outfile = outfile,
  x = "world",
  y = "ExTera"
)

readLines(outfile, warn = FALSE)

Method render_to_string()

Render specified template to string.

Usage

ExTera$render_to_string(template, ...)

Arguments

template

character scalar, the name of the template to render.

...

specify context as key-value pairs where key is the template variable and value is the data to inject.

Details

All context elements must be named.

Returns

Rendered string with class TeraString for "pretty" printing.

Examples

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

tera$render_to_string(
  "hello-world",
  x = "world",
  y = "ExTera"
)

Method autoescape_on()

Turn on autoescaping of HTML. Autoescaping is on by default.

Usage

ExTera$autoescape_on()

Details

Autoescaping only applies to templates whose names end with ".html", ".htm", or ".xml".

Returns

Self (invisibly)

Examples

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  "hello-world.html" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

# not recognized as html
tera$render_to_string(
  "hello-world",
  x = "&world",
  y = "an apostrophe, '"
)

# html
tera$render_to_string(
  "hello-world.html",
  x = "&world",
  y = "an apostrophe, '"
)

Method autoescape_off()

Turn off autoescaping of HTML.

Usage

ExTera$autoescape_off()

Details

Autoescaping is on by default.

Returns

Self (invisibly)

Examples

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world.html" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

tera$autoescape_off()

tera$render_to_string(
  "hello-world.html",
  x = "&world",
  y = "an apostrophe, '"
)

Examples


## ------------------------------------------------
## Method `ExTera$new`
## ------------------------------------------------

# initialize ExTera with empty library
tera <- ExTera$new()
tera
#> 
#> ── ExTera ──
#> 
#> Template library:

# initialize ExTera from directory with glob
template_dir <- file.path(tempdir(), "templates")

dir.create(template_dir)

tmp <- file.path(
  template_dir,
  "hello-world-template.html"
)

writeLines(
  text = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  con = tmp
)

tera <- ExTera$new(dir = file.path(template_dir, "*.html"))
tera
#> 
#> ── ExTera ──
#> 
#> Template library:
#> • hello-world-template.html

## ------------------------------------------------
## Method `ExTera$add_file_templates`
## ------------------------------------------------

tera <- ExTera$new()

writeLines(
  '<p>Hello {{ x }}. This is {{ y }}.</p>',
  con = file.path(tempdir(), "hello-world.html")
)

writeLines(
  '<img src="{{ img_src }}">',
  con = file.path(tempdir(), "img-src.html")
)

tera$add_file_templates(
  "hello-world" = file.path(tempdir(), "hello-world.html"),
  "img-src" = file.path(tempdir(), "img-src.html")
)

tera
#> 
#> ── ExTera ──
#> 
#> Template library:
#> • img-src
#> • hello-world

## ------------------------------------------------
## Method `ExTera$add_string_templates`
## ------------------------------------------------

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  "img-src" = '<img src="{{ img_src }}">'
)

tera
#> 
#> ── ExTera ──
#> 
#> Template library:
#> • img-src
#> • hello-world

## ------------------------------------------------
## Method `ExTera$list_templates`
## ------------------------------------------------

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  "img-src" = '<img src="{{ img_src }}">'
)

tera$list_templates()

## ------------------------------------------------
## Method `ExTera$render`
## ------------------------------------------------

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

outfile <- file.path(tempdir(), "rendered-hello-world.html")

tera$render(
  "hello-world",
  outfile = outfile,
  x = "world",
  y = "ExTera"
)

readLines(outfile, warn = FALSE)
#> [1] "<p>Hello world. This is ExTera.</p>"

## ------------------------------------------------
## Method `ExTera$render_to_string`
## ------------------------------------------------

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

tera$render_to_string(
  "hello-world",
  x = "world",
  y = "ExTera"
)
#> Rendered hello-world template:
#> 
#> <p>Hello world. This is ExTera.</p>
#> 

## ------------------------------------------------
## Method `ExTera$autoescape_on`
## ------------------------------------------------

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world" = '<p>Hello {{ x }}. This is {{ y }}.</p>',
  "hello-world.html" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

# not recognized as html
tera$render_to_string(
  "hello-world",
  x = "&world",
  y = "an apostrophe, '"
)
#> Rendered hello-world template:
#> 
#> <p>Hello &world. This is an apostrophe, '.</p>
#> 

# html
tera$render_to_string(
  "hello-world.html",
  x = "&world",
  y = "an apostrophe, '"
)
#> Rendered hello-world.html template:
#> 
#> <p>Hello &amp;world. This is an apostrophe, &#x27;.</p>
#> 

## ------------------------------------------------
## Method `ExTera$autoescape_off`
## ------------------------------------------------

tera <- ExTera$new()

tera$add_string_templates(
  "hello-world.html" = '<p>Hello {{ x }}. This is {{ y }}.</p>'
)

tera$autoescape_off()

tera$render_to_string(
  "hello-world.html",
  x = "&world",
  y = "an apostrophe, '"
)
#> Rendered hello-world.html template:
#> 
#> <p>Hello &world. This is an apostrophe, '.</p>
#>