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changelog.md

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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.
  • 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:

.. code-block:: nim

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:

.. code-block:: nim

t[ti] = if exp_negative: '-' else: '+'; inc(ti)

This now needs to be written as:

.. code-block:: nim

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:

.. code-block:: nim

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.

  • 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.