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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2002-2013, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala
/** This class provides the basic mechanism to do String Interpolation.
* String Interpolation allows users
* to embed variable references directly in *processed* string literals.
* Here's an example:
* {{{
* val name = "James"
* println(s"Hello, $name") // Hello, James
* }}}
*
* Any processed string literal is rewritten as an instantiation and
* method call against this class. For example:
* {{{
* s"Hello, $name"
* }}}
*
* is rewritten to be:
*
* {{{
* StringContext("Hello, ", "").s(name)
* }}}
*
* By default, this class provides the `raw`, `s` and `f` methods as
* available interpolators.
*
* To provide your own string interpolator, create an implicit class
* which adds a method to `StringContext`. Here's an example:
* {{{
* implicit class JsonHelper(val sc: StringContext) extends AnyVal {
* def json(args: Any*): JSONObject = ...
* }
* val x: JSONObject = json"{ a: $a }"
* }}}
*
* Here the `JsonHelper` extenion class implicitly adds the `json` method to
* `StringContext` which can be used for `json` string literals.
*
* @since 2.10.0
* @param parts The parts that make up the interpolated string,
* without the expressions that get inserted by interpolation.
*/
case class StringContext(parts: String*) {
import StringContext._
/** Checks that the length of the given argument `args` is one less than the number
* of `parts` supplied to the enclosing `StringContext`.
* @param `args` The arguments to be checked.
* @throws An `IllegalArgumentException` if this is not the case.
*/
def checkLengths(args: Seq[Any]): Unit =
if (parts.length != args.length + 1)
throw new IllegalArgumentException("wrong number of arguments for interpolated string")
/** The simple string interpolator.
*
* It inserts its arguments between corresponding parts of the string context.
* It also treats standard escape sequences as defined in the Scala specification.
* Here's an example of usage:
* {{{
* val name = "James"
* println(s"Hello, $name") // Hello, James
* }}}
* In this example, the expression $name is replaced with the `toString` of the
* variable `name`.
* The `s` interpolator can take the `toString` of any arbitrary expression within
* a `${}` block, for example:
* {{{
* println(s"1 + 1 = ${1 + 1}")
* }}}
* will print the string `1 + 1 = 2`.
*
* @param `args` The arguments to be inserted into the resulting string.
* @throws An `IllegalArgumentException`
* if the number of `parts` in the enclosing `StringContext` does not exceed
* the number of arguments `arg` by exactly 1.
* @throws A `StringContext.InvalidEscapeException` if a `parts` string contains a backslash (`\`) character
* that does not start a valid escape sequence.
*/
def s(args: Any*): String = standardInterpolator(treatEscapes, args)
/** The raw string interpolator.
*
* It inserts its arguments between corresponding parts of the string context.
* As opposed to the simple string interpolator `s`, this one does not treat
* standard escape sequences as defined in the Scala specification.
*
* For example, the raw processed string `raw"a\nb"` is equal to the scala string `"a\\nb"`.
*
* ''Note:'' Even when using the raw interpolator, Scala will preprocess unicode escapes.
* For example:
* {{{
* scala> raw"\u005cu0025"
* res0: String = #
* }}}
*
* @param `args` The arguments to be inserted into the resulting string.
* @throws An `IllegalArgumentException`
* if the number of `parts` in the enclosing `StringContext` does not exceed
* the number of arguments `arg` by exactly 1.
* @throws A `StringContext.InvalidEscapeException` if a `parts` string contains a backslash (`\`) character
* that does not start a valid escape sequence.
*/
def raw(args: Any*): String = standardInterpolator(identity, args)
def standardInterpolator(process: String => String, args: Seq[Any]): String = {
checkLengths(args)
val pi = parts.iterator
val ai = args.iterator
val bldr = new java.lang.StringBuilder(process(pi.next()))
while (ai.hasNext) {
bldr append ai.next
bldr append process(pi.next())
}
bldr.toString
}
/** The formatted string interpolator.
*
* It inserts its arguments between corresponding parts of the string context.
* It also treats standard escape sequences as defined in the Scala specification.
* Finally, if an interpolated expression is followed by a `parts` string
* that starts with a formatting specifier, the expression is formatted according to that
* specifier. All specifiers allowed in Java format strings are handled, and in the same
* way they are treated in Java.
*
* For example:
* {{{
* val height = 1.9d
* val name = "James"
* println(f"$name%s is $height%2.2f meters tall") // James is 1.90 meters tall
* }}}
*
* @param `args` The arguments to be inserted into the resulting string.
* @throws An `IllegalArgumentException`
* if the number of `parts` in the enclosing `StringContext` does not exceed
* the number of arguments `arg` by exactly 1.
* @throws A `StringContext.InvalidEscapeException` if a `parts` string contains a backslash (`\`) character
* that does not start a valid escape sequence.
*
* Note: The `f` method works by assembling a format string from all the `parts` strings and using
* `java.lang.String.format` to format all arguments with that format string. The format string is
* obtained by concatenating all `parts` strings, and performing two transformations:
*
* 1. Let a _formatting position_ be a start of any `parts` string except the first one.
* If a formatting position does not refer to a `%` character (which is assumed to
* start a format specifier), then the string format specifier `%s` is inserted.
*
* 2. Any `%` characters not in formatting positions are left in the resulting
* string literally. This is achieved by replacing each such occurrence by the
* format specifier `%%`.
*/
// The implementation is hardwired to `scala.tools.reflect.MacroImplementations.macro_StringInterpolation_f`
// Using the mechanism implemented in `scala.tools.reflect.FastTrack`
def f(args: Any*): String = macro ???
}
object StringContext {
/** An exception that is thrown if a string contains a backslash (`\`) character
* that does not start a valid escape sequence.
* @param str The offending string
* @param idx The index of the offending backslash character in `str`.
*/
class InvalidEscapeException(str: String, idx: Int)
extends IllegalArgumentException("invalid escape character at index "+idx+" in \""+str+"\"")
/** Expands standard Scala escape sequences in a string.
* Escape sequences are:
* control: `\b`, `\t`, `\n`, `\f`, `\r`
* escape: `\\`, `\"`, `\'`
* octal: `\d` `\dd` `\ddd` where `d` is an octal digit between `0` and `7`.
*
* @param str A string that may contain escape sequences
* @return The string with all escape sequences expanded.
*/
def treatEscapes(str: String): String = {
lazy val bldr = new java.lang.StringBuilder
val len = str.length
var start = 0
var cur = 0
var idx = 0
def output(ch: Char) = {
bldr.append(str, start, cur)
bldr append ch
start = idx
}
while (idx < len) {
cur = idx
if (str(idx) == '\\') {
idx += 1
if (idx >= len) throw new InvalidEscapeException(str, cur)
if ('0' <= str(idx) && str(idx) <= '7') {
val leadch = str(idx)
var oct = leadch - '0'
idx += 1
if (idx < len && '0' <= str(idx) && str(idx) <= '7') {
oct = oct * 8 + str(idx) - '0'
idx += 1
if (idx < len && leadch <= '3' && '0' <= str(idx) && str(idx) <= '7') {
oct = oct * 8 + str(idx) - '0'
idx += 1
}
}
output(oct.toChar)
} else {
val ch = str(idx)
idx += 1
output {
ch match {
case 'b' => '\b'
case 't' => '\t'
case 'n' => '\n'
case 'f' => '\f'
case 'r' => '\r'
case '\"' => '\"'
case '\'' => '\''
case '\\' => '\\'
case _ => throw new InvalidEscapeException(str, cur)
}
}
}
} else {
idx += 1
}
}
if (start == 0) str
else bldr.append(str, start, idx).toString
}
}
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