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v0.18.0 - dd/mm/yyyy

Changes affecting backwards compatibility

  • Arrays of char cannot be converted to cstring anymore, pointers to arrays of char can! This means $ for arrays can finally exist in system.nim and do the right thing.
  • echo now works with strings that contain \0 (the binary zero is not shown) and nil strings are equal to empty strings.
  • JSON: Deprecated getBVal, getFNum, and getNum in favour to getBool, getFloat, getBiggestInt. Also getInt procedure was added.
  • reExtended is no longer default for the re constructor in the re module.
  • newAsyncSocket taking an AsyncFD now runs setBlocking(false) on the fd.
  • The ReadyKey type in the selectors module now contains an errorCode field to help distinguish between Event.Error events.
  • Implemented an accept proc that works on a SocketHandle in nativesockets.
  • Implemented getIoHandler proc in the asyncdispatch module that allows you to retrieve the underlying IO Completion Port or Selector[AsyncData] object in the specified dispatcher.
  • The overloading rules changed slightly so that constrained generics are preferred over unconstrained generics. (Bug #6526)
  • It is now possible to forward declare object types so that mutually recursive types can be created across module boundaries. See package level objects for more information.
  • The unary < is now deprecated, for .. < use ..< for other usages use the pred proc.
  • We changed how array accesses "from backwards" like a[^1] or a[0..^1] are implemented. These are now implemented purely in system.nim without compiler support. There is a new "heterogenous" slice type system.HSlice that takes 2 generic parameters which can be BackwardsIndex indices. BackwardsIndex is produced by system.^. This means if you overload [] or []= you need to ensure they also work with system.BackwardsIndex (if applicable for the accessors).
  • mod and bitwise and do not produce range subtypes anymore. This turned out to be more harmful than helpful and the language is simpler without this special typing rule.
  • Added algorithm.rotateLeft.
  • rationals.toRational now uses an algorithm based on continued fractions. This means its results are more precise and it can't run into an infinite loop anymore.
  • Added typetraits.$ as an alias for typetraits.name.
  • os.getEnv now takes an optional default parameter that tells getEnv what to return if the environment variable does not exist.
  • Bodies of for loops now get their own scope:
  # now compiles:
  for i in 0..4:
    let i = i + 1
    echo i
  • The parsing rules of if expressions were changed so that multiple statements are allowed in the branches. We found few code examples that now fail because of this change, but here is one:
  t[ti] = if exp_negative: '-' else: '+'; inc(ti)

This now needs to be written as:

  t[ti] = (if exp_negative: '-' else: '+'); inc(ti)
  • To make Nim even more robust the system iterators .. and countup now only accept a single generic type T. This means the following code doesn't die with an "out of range" error anymore:
  var b = 5.Natural
  var a = -5
  for i in a..b:
    echo i

  • formatFloat/formatBiggestFloat now support formatting floats with zero precision digits. The previous precision = 0 behavior (default formatting) is now available via precision = -1.

  • The nim doc command is now an alias for nim doc2, the second version of the documentation generator. The old version 1 can still be accessed via the new nim doc0 command.

  • Added system.getStackTraceEntries that allows you to access the stack trace in a structured manner without string parsing.

  • Added sequtils.mapLiterals for easier construction of array and tuple literals.

  • Added parseutils.parseSaturatedNatural.

  • atomic and generic are no longer keywords in Nim. generic used to be an alias for concept, atomic was not used for anything.

  • Moved from stdlib into Nimble packages:

  • Added system.runnableExamples to make examples in Nim's documentation easier to write and test. The examples are tested as the last step of nim doc.

  • Nim's rst2html command now supports the testing of code snippets via an RST extension that we called :test:::

      .. code-block:: nim
      :test:
    # shows how the 'if' statement works
    if true: echo "yes"

  • The [] proc for strings now raises an IndexError exception when the specified slice is out of bounds. See issue #6223 for more details. You can use substr(str, start, finish) to get the old behaviour back, see this commit for an example.

  • strutils.split and strutils.rsplit with an empty string and a separator now returns that empty string. See issue #4377.

  • The experimental overloading of the dot . operators now take an untyped``` parameter as the field name, it used to be a static[string]. You can use when defined(nimNewDot)`` to make your code work with both old and new Nim versions. See special-operators for more information.

  • Added macros.unpackVarargs.

  • The memory manager now uses a variant of the TLSF algorithm that has much better memory fragmentation behaviour. According to http://www.gii.upv.es/tlsf/ the maximum fragmentation measured is lower than 25%. As a nice bonus alloc and dealloc became O(1) operations.

  • The behavior of $ has been changed for all standard library collections. The collection-to-string implementations now perform proper quoting and escaping of strings and chars.

  • The random procs in random.nim have all been deprecated. Instead use the new rand procs. The module now exports the state of the random number generator as type Rand so multiple threads can easily use their own random number generators that do not require locking. For more information about this rename see issue #6934

  • The compiler is now more consistent in its treatment of ambiguous symbols: Types that shadow procs and vice versa are marked as ambiguous (bug #6693).

  • yield (or await which is mapped to yield) never worked reliably in an array, seq or object constructor and is now prevented at compile-time.

  • For string formatting / interpolation a new module called strformat has been added to the stdlib.

  • codegenDecl pragma now works for the JavaScript backend. It returns an empty string for function return type placeholders.

  • Asynchronous programming for the JavaScript backend using the asyncjs module.

  • Extra semantic checks for procs with noreturn pragma: return type is not allowed, statements after call to noreturn procs are no longer allowed.

  • Noreturn proc calls and raising exceptions branches are now skipped during common type deduction in if and case expressions. The following code snippets now compile:

import strutils
let str = "Y"
let a = case str:
  of "Y": true
  of "N": false
  else: raise newException(ValueError, "Invalid boolean")
let b = case str:
  of nil, "": raise newException(ValueError, "Invalid boolean")
  elif str.startsWith("Y"): true
  elif str.startsWith("N"): false
  else: false
let c = if str == "Y": true
  elif str == "N": false
  else:
    echo "invalid bool"
    quit("this is the end")
  • Proc toCountTable now produces a CountTable with values correspoding to the number of occurrences of the key in the input. It used to produce a table with all values set to 1.

Counting occurrences in a sequence used to be:

let mySeq = @[1, 2, 1, 3, 1, 4]
var myCounter = initCountTable[int]()

for item in mySeq:
  myCounter.inc item

Now, you can simply do:

let
  mySeq = @[1, 2, 1, 3, 1, 4]
  myCounter = mySeq.toCountTable()

  • Added support for casting between integers of same bitsize in VM (compile time and nimscript). This allow to among other things to reinterpret signed integers as unsigned.

  • Pragmas now support call syntax, for example: {.exportc"myname".} and {.exportc("myname").}

  • Custom pragmas are now supported using pragma pragma, please see language manual for details

  • Added True Color support for some terminals Example:

import colors, terminal

const Nim = "Efficient and expressive programming."

var
  fg = colYellow
  bg = colBlue
  int = 1.0

enableTrueColors()

for i in 1..15:
  styledEcho bgColor, bg, fgColor, fg, Nim, resetStyle
  int -= 0.01
  fg = intensity(fg, int)

setForegroundColor colRed
setBackgroundColor colGreen
styledEcho "Red on Green.", resetStyle

  • If you use --dynlibOverride:ssl with OpenSSL 1.0.x, you now have to define openssl10 symbol (-d:openssl10). By default OpenSSL 1.1.x is assumed.

  • writeStackTrace is now proclaimed to have no IO effect (even though it does) so that it is more useful for debugging purposes.

  • \n is now only the single line feed character like in most other programming languages. The new platform specific newline escape sequence is written as \p. This change only affects the Windows platform.