R: Bundling Sass layers

sass_layer {sass} | R Documentation

## Bundling Sass layers

### Description

Sass layers are a way to group a set of related Sass variable definitions, function/mixin declarations, and CSS rules into a single object. Use `sass_layer()` to create these objects, and `sass_bundle()` to combine two or more layers or bundles objects into a Sass bundle; this ability to be merged is the main benefit of using Sass layers versus lower-level forms of sass input. At a later time, Sass layers may be removed from Sass bundles by referencing the same name that was used when creating the Sass bundle.

### Usage

    sass_layer(
      defaults = NULL,
      declarations = NULL,
      rules = NULL,
      html_deps = NULL,
      file_attachments = character(0),
      tags = NULL
    )

    sass_bundle(...)

    sass_bundle_remove(bundle, name)

    is_sass_bundle(x)

### Arguments

`defaults` | A suitable `as_sass()` `input`. Intended for declaring variables with `!default`. When layers are combined, defaults are merged in reverse order; that is, `sass_bundle(layer1, layer2)` will include `layer2$defaults` before `layer1$defaults`.
`declarations` | A suitable `as_sass()` `input`. Intended for function and mixin declarations, and variable declarations without `!default`; not intended for actual CSS rules. These will be merged in forward order; that is, `sass_bundle(layer1, layer2)` will include `layer1$declarations` before `layer2$declarations`.
`rules` | A suitable `as_sass()` `input`. Intended for actual CSS rules. These will be merged in forward order; that is, `sass_bundle(layer1, layer2)` will include `layer1$rules` before `layer2$rules`.
`html_deps` | An HTML dependency (or a list of them).
`file_attachments` | A named character vector, representing file assets that are referenced (using relative paths) from the sass in this layer. The vector names should be a relative path, and the corresponding vector values should be absolute paths to files or directories that exist; at render time, each value will be copied to the relative path indicated by its name. (For directories, the contents of the source directory will be copied into the destination directory; the directory itself will not be copied.) You can also omit the name, in which case that file or directory will be copied directly into the output directory.
`tags` | Deprecated. Preserve meta information using a key in `sass_bundle(KEY = val)`. preserve simple metadata as layers are merged.
`...` | A collection of `sass_layer()`s and/or objects that `as_sass()` understands. Arguments should be provided in reverse priority order: defaults, declarations, and rules in later layers will take precedence over those of previous layers. Non-layer values will be converted to layers by calling `sass_layer(rules = ...)`.
`bundle` | Output value from `sass_layer()` or `sass_bundle()`
`name` | If a Sass layer name is contained in `name`, the matching Sass layer will be removed from the `bundle`
`x` | object to inspect

### Functions

- `sass_layer`: Compose the parts of a single Sass layer. Object returned is a `sass_bundle()` with a single Sass layer

- `sass_bundle`: Collect `sass_bundle()` and/or `sass_layer()` objects. Unnamed Sass bundles will be concatenated together, preserving their internal name structures. Named Sass bundles will be condensed into a single Sass layer for easier removal from the returned Sass bundle.

- `sass_bundle_remove`: Remove a whole `sass_layer()` from a `sass_bundle()` object.

- `is_sass_bundle`: Check if `x` is a Sass bundle object

### Examples

    blue <- list(color = "blue !default")
    red <- list(color = "red !default")
    green <- list(color = "green !default")

    # a sass_layer() by itself is not very useful, it just defines some
    # SASS to place before (defaults) and after (declarations, rules)
    core <- sass_layer(defaults = blue, rules = "body { color: $color; }")
    core
    sass(core)

    # However, by stacking sass_layer()s, we have ability to place
    # SASS both before and after some other sass (e.g., core)
    # Here we place a red default _before_ the blue default and export the
    # color SASS variable as a CSS variable _after_ the core
    red_layer <- sass_layer(red, rules = ":root{ --color: #{$color}; }")
    sass(sass_bundle(core, red_layer))
    sass(sass_bundle(core, red_layer, sass_layer(green)))

    # Example of merging layers and removing a layer
    # Remember to name the layers that are removable
    core_layers <- sass_bundle(core, red = red_layer, green = sass_layer(green))
    core_layers # pretty printed for console
    core_slim <- sass_bundle_remove(core_layers, "red")
    sass(core_slim)

    # File attachment example: Create a checkboard pattern .png, then
    # use it from a sass layer

    tmp_png <- tempfile(fileext = ".png")
    grDevices::png(filename = tmp_png, width = 20, height = 20,
      bg = "transparent", antialias = "none")
    par(mar = rep_len(0,4), xaxs = "i", yaxs = "i")
    plot.new()
    rect(c(0,0.5), c(0,0.5), c(0.5,1), c(0.5,1), col = "#00000044", border=NA)
    dev.off()

    layer <- sass_layer(
      rules = ".bg-check { background-image: url(images/demo_checkboard_bg.png) }",
      file_attachments = c("images/demo_checkboard_bg.png" = tmp_png)
    )

    output_path <- tempfile(fileext = ".css")
    sass(layer, output = output_path, write_attachments = TRUE)

[Package sass version 0.3.1 Index]