Boilerplate is an sbt-plugin that generates stubs for code which has to be expanded
for all numbers of arguments from 1 to 22. This is sometimes necessary to support
all of the TupleX or FunctionX generically.
The plugin defines a simple template language for this purpose.
The template file contains mostly literal code with some control characters guiding the expansion. Expansion follows these rules:
- The current number of arguments
iis initialized to 22. - Code embraced in
[#and#]is copieditimes and the expansion is applied recursively withibeing set accordingly.- It is possible to define a custom separator
between the copied instances by putting the separator text between the
#and the]of the closing bracket. If no separator is supplied", "is assumed. - You can specify a custom range
ishould iterate through by placing a term of the form<start>..<end>between the starting[and#of an expansion. Eitherstartorendcan be omitted in which case the defaults are assumed.
- It is possible to define a custom separator
between the copied instances by putting the separator text between the
- Everywhere digit
1is replaced byi, digit0is replaced byi - 1, and digit2is replaced byi + 1unless the digit is prefixed with##. - To encode the sharp
'#'character precede it with a backslash e.g."\#".
Consider the task is to provide overloads for a function which can apply a function to a tuple for all numbers of arguments from 1 to 22.
Start by writing out the function for only one argument:
def applyFunc[P1, R](input: Tuple1[P1], func: (P1) => R): R =
func(input._1)
For the function to be copied for each possible number of arguments, enclose it in [#
and #] (the newline between the closing # and ] defines that instances should be
separated by newline and not by the default ", "):
[#def applyFunc[P1, R](input: Tuple1[P1], func: (P1) => R): R =
func(input._1)#
]
This will already expand to:
def applyFunc[P1, R](input: Tuple1[P1], func: (P1) => R): R =
func(input._1)
def applyFunc[P2, R](input: Tuple2[P2], func: (P2) => R): R =
func(input._2)
def applyFunc[P3, R](input: Tuple3[P3], func: (P3) => R): R =
func(input._3)
def applyFunc[P4, R](input: Tuple4[P4], func: (P4) => R): R =
func(input._4)
// ...
This is not yet what we want, because we P1 to expand to
P1, P2, ..., Pi and input._1 to input._1, input._2, ..., input._i. So we embrace the
parts to expand another time:
[#def applyFunc[[#P1#], R](input: Tuple1[[#P1#]], func: ([#P1#]) => R): R =
func([#input._1#])#
]
This now expands correctly to
def applyFunc[P1, R](input: Tuple1[P1], func: (P1) => R): R =
func(input._1)
def applyFunc[P1, P2, R](input: Tuple2[P1, P2], func: (P1, P2) => R): R =
func(input._1, input._2)
def applyFunc[P1, P2, P3, R](input: Tuple3[P1, P2, P3], func: (P1, P2, P3) => R): R =
func(input._1, input._2, input._3)
def applyFunc[P1, P2, P3, P4, R](input: Tuple4[P1, P2, P3, P4], func: (P1, P2, P3, P4) => R): R =
func(input._1, input._2, input._3, input._4)
sbt-boilerplate currently supports sbt 1.x.
Put
addSbtPlugin("com.github.sbt" % "sbt-boilerplate" % "0.7.0")
into your plugins.sbt. sbt-boilerplate is an AutoPlugin which needs to be enabled using
enablePlugins(spray.boilerplate.BoilerplatePlugin)The templates have to be put into the src/main/boilerplate directory and the file name
must end with .template. The generated files will be put into the same hierarchy as they
appear in src/main/boilerplate with the .template extension stripped off. If the stripped
filename has no extension ".scala" is added automatically.
- Instances for zero arguments have to be supplied manually.
- akka uses sbt-boilerplate for akka-actor, akka-stream, and akka-http
- spray-routing uses sbt-boilerplate to provide conversions to/from HLists
- product-collections
Copyright (c) 2012-2016 Johannes Rudolph
Published under the BSD 2-Clause License.
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