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Version 0.14.0 released

It's been a while since the last release, but we've been very busy in the meantime. In addition to working on Nim we have started a BountySource campaign and announced the pre-release of a new Nim book titled Nim in Action. Our BountySource campaign has already been very successful, helping us raise enough funds to surpass 4 of our monthly goals. The companies and individuals that made this possible are listed on our brand new sponsors page.

This release includes over 260 bug fixes. As mentioned in the previous release announcement, one of the focuses of this release was going to be improvements to the GC. Indeed, the most prominent fixes are related to the GC not collecting cycles properly. This was a major problem that was triggered typically when applications using asynchronous I/O were left running for long periods of time.

There have also been many fixes to the way that the compiler sources are installed. Some applications such as Nimble depend on these sources and they are now included in the release tarballs. This should fix many of the problems that users experienced trying to compile the Nimble package manager.

Finally, you will find multiple changes in the standard library. Some of which unfortunately affects backwards compatibility. This includes the random procedures being moved to a new random module, HTTP headers being stored in a new HttpHeaders object and the round procedure in the math module being changed to return a float instead of an int. You can find a full list of such changes below.

Together with the new release of Nim, we are also releasing a new version of Nimble. The release notes for it are available on GitHub.

As always you can download the latest version of Nim from the download page.

We hope that you will like this new release. Let us know if you run into any trouble, have any questions or want to give some feedback. You can get in touch with us on the Forum, IRC, Twitter, or via email

Happy coding!

Changes affecting backwards compatibility

  • --out and --nimcache command line arguments are now relative to current directory. Previously they were relative to project directory.
  • The json module now stores the name/value pairs in objects internally as a hash table of type fields*: Table[string, JsonNode] instead of a sequence. This means that order is no longer preserved. When using the table.mpairs iterator only the returned values can be modified, no longer the keys.
  • The deprecated Nim shebang notation #! was removed from the language. Use #? instead.
  • Typeless parameters have been removed from the language since it would clash with using.
  • Procedures in mersenne.nim (Mersenne Twister implementation) no longer accept and produce int values which have platform-dependent size - they use uint32 instead.
  • The strutils.unindent procedure has been rewritten. Its parameters now match the parameters of strutils.indent. See issue #4037 for more details.
  • The matchers module has been deprecated. See issue #2446 for more details.
  • The json.[] no longer returns nil when a key is not found. Instead it raises a KeyError exception. You can compile with the -d:nimJsonGet flag to get a list of usages of [], as well as to restore the operator's previous behaviour.
  • When using useMalloc, an additional header containing the size of the allocation will be allocated, to support zeroing memory on realloc as expected by the language. With this change, alloc and dealloc are no longer aliases for malloc and free - use c_malloc and c_free if you need that.
  • The json.% operator is now overloaded for object, ref object and openarray[T].
  • The procs related to random number generation in math.nim have been moved to its own random module and been reimplemented in pure Nim.
  • The path handling changed. The project directory is not added to the search path automatically anymore. Add this line to your project's config to get back the old behaviour: --path:"$projectdir". (The compiler replaces $projectdir with your project's absolute directory when compiling, so you don't need to replace $projectdir by your project's actual directory!). See issue #546 and this forum thread for more information.
  • The round function in math.nim now returns a float and has been corrected such that the C implementation always rounds up from .5 rather than changing the operation for even and odd numbers.
  • The round function now accepts a places argument to round to a given number of places (e.g. round 4.35 to 4.4 if places is 1).
  • In strutils.nim, formatSize now returns a number representing the size in conventional decimal format (e.g. 2.234GB meaning 2.234 GB rather than meaning 2.285 GB as in the previous implementation). By default it also uses IEC prefixes (KiB, MiB) etc and optionally uses colloquial names (kB, MB etc) and the (SI-preferred) space.
  • The == operator for cstring now implements a value comparison for the C backend (using strcmp), not reference comparisons anymore. Convert the cstrings to pointers if you really want reference equality for speed.
  • HTTP headers are now stored in a HttpHeaders object instead of a StringTableRef. This object allows multiple values to be associated with a single key. A new httpcore module implements it and it is used by both asynchttpserver and httpclient.

The using statement

The using statement now has a different meaning.

In version 0.13.0, it was used to provide syntactic convenience for procedures that heavily use a single contextual parameter. For example:

var socket = newSocket()
using socket

connect("", Port(80))
send("GET / HTTP/1.1\c\l")

The connect and send calls are both transformed so that they pass socket as the first argument:

var socket = newSocket()

socket.connect("", Port(80))
socket.send("GET / HTTP/1.1\c\l")

Take a look at the old version of the manual to learn more about the old behaviour.

In 0.14.0, the using statement instead provides a syntactic convenience for procedure definitions where the same parameter names and types are used repeatedly. For example, instead of writing:

proc foo(c: Context; n: Node) = ...
proc bar(c: Context; n: Node, counter: int) = ...
proc baz(c: Context; n: Node) = ...

You can simply write:

  c: Context
  n: Node
  counter: int

proc foo(c, n) = ...
proc bar(c, n, counter) = ...
proc baz(c, n) = ...

Again, the manual has more details.

You can still achieve a similar effect to what the old using statement tried to achieve by using the new experimental this pragma, documented here.

Generic type classes

Generic type classes are now handled properly in the compiler, but this means code like the following does not compile any longer:

  Vec3[T] = distinct array[3, T]

proc vec3*[T](a, b, c: T): Vec3[T] = Vec3([a, b, c])

While every Vec3[T] is part of the Vec3 type class, the reverse is not true, not every Vec3 is a Vec3[T]. Otherwise there would be a subtype relation between Vec3[int] and Vec3[float] and there is none for Nim. The fix is to write this instead:

  Vec3[T] = distinct array[3, T]

proc vec3*[T](a, b, c: T): Vec3[T] = Vec3[T]([a, b, c])

Note that in general we don't advise to use distinct array, use object instead.

Library Additions

  • The rlocks module has been added providing a reentrant lock synchronization primitive.
  • A generic "sink operator" written as &= has been added to the

system and the net modules. This operator is similar to the C++ << operator which writes data to a stream.

  • Added strscans module that implements a scanf for easy input extraction.
  • Added a version of parseutils.parseUntil that can deal with a string until token. The other versions are for char and set[char].
  • Added splitDecimal to math.nim to split a floating point value into an integer part and a floating part (in the range -1<x<1).
  • Added trimZeros to strutils.nim to trim trailing zeros in a floating point number.
  • Added formatEng to strutils.nim to format numbers using engineering notation.

Compiler Additions

  • Added a new --noCppExceptions switch that allows to use default exception handling (no throw or try/catch generated) when compiling to C++ code.

Language Additions

  • Nim now supports a .this pragma for more notational convenience. See automatic-self-insertions for more information.
  • Nim now supports a different using statement for more convenience. Consult using-statement for more information.
  • include statements are not restricted to top level statements anymore.


The list below has been generated based on the commits in Nim's git repository. As such it lists only the issues which have been closed via a commit, for a full list see this link on Github.

  • Fixed "Calling generic templates with explicit generic arguments crashes compiler" (#3496)
  • Fixed "JS backend - strange utf-8 handling" (#3714)
  • Fixed "execvpe is glibc specific" (#3759)
  • Fixed "GC stack overflow with in data structures with circular references." (#1895)
  • Fixed "Internal compiler error in genTraverseProc" (#3794)
  • Fixed "unsafeAddr fails in generic context" (#3736)
  • Fixed "Generic converters produce internal errors" (#3799)
  • Fixed "Cannot have two anonymous iterators in one proc" (#3788)
  • Fixed "pure/net.nim fails to compile with --taintMode:on on HEAD" (#3789)
  • Fixed "Using break inside iterator may produce memory/resource leak" (#3802)
  • Fixed "--out and --nimcache wrong paths" (#3871)
  • Fixed "Release 0.13.0: documentation build failure" (#3823)
  • Fixed "https post request" (#3895)
  • Fixed "writeFile regression in nimscript" (#3901)
  • Fixed "Cannot convert variables to int16 at compile time" (#3916)
  • Fixed "Error in concepts when using functions on typedesc" (#3686)
  • Fixed "Multiple generic table types with different type signatures lead to compilation errors." (#3669)
  • Fixed "Explicit arguments with overloaded procedure?" (#3836)
  • Fixed "doc2 generates strange output for proc generated by template" (#3868)
  • Fixed "Passing const value as static[] argument to immediate macro leads to infinite memory consumption by compiler" (#3872)
  • Fixed "..< is not happy with BiggestInt from intVal" (#3767)
  • Fixed "stdtmpl filter does not support anything apart from '#' metachar" (#3924)
  • Fixed "lib/pure/net: Can't bind to ports >= 32768" (#3484)
  • Fixed "int and float assignment compatibility badly broken for generics" (#3998)
  • Fixed "Adding echo statement causes "type mismatch" error" (#3975)
  • Fixed "Dynlib error messages should be written to stderr, not stdout" (#3987)
  • Fixed "Tests regressions while using the devel branch" (#4005)
  • Fixed "Lambda lifting bug: wrong c code generation" (#3995)
  • Fixed "VM crashes in asgnComplex" (#3973)
  • Fixed "Unknown opcode opcNGetType" (#1152)
  • Fixed "& operator mutates first operand when used in compileTime proc while assigning result to seq" (#3804)
  • Fixed "''nil' statement is deprecated' in macro" (#3561)
  • Fixed "vm crash when accessing seq with mitems iterator" (#3731)
  • Fixed "mitems or mpairs does not work for seq[NimNode] or array[T,NimNode] in a macro" (#3859)
  • Fixed "passing "proc ,`()" to nim check causes an infinite loop" (`#4036)
  • Fixed "--dynlibOverride does not work with {.push dynlib: name.}" (#3646)
  • Fixed "system.readChars fails on big len" (#3752)
  • Fixed "strutils.unindent" (#4037)
  • Fixed "Compiler's infinite recursion in generic resolution" (#2006)
  • Fixed "Linux: readLineFromStdin calls quit(0) upon EOF" (#3159)
  • Fixed "Forum sign up not possible" (#2446)
  • Fixed "Json module - SIGSEGV if key not exists" (#3107)
  • Fixed "About asyncdispatch.await and exception" (#3964)
  • Fixed "Need testcase for JS backend to ensure closure callbacks don't break" (#3132)
  • Fixed "Unexpected behaviour of C++ templates in conjunction with N_NIMCALL" (#4093)
  • Fixed "SIGSEGV at compile time when using a compileTime variable as counter" (#4097)
  • Fixed "Compiler crash issue on 32-bit machines only" (#4089)
  • Fixed "type mismatch: got (<type>) but expected 'outType' in mapIt" (#4124)
  • Fixed "Generic type constraints broken?" (#4084)
  • Fixed "Invalid C code generated" (#3544)
  • Fixed "An exit variable in proc shadows exit function called by quit()" (#3471)
  • Fixed "ubuntu 16.04 build error" (#4144)
  • Fixed "Ambiguous identifier error should list all possible qualifiers" (#177)
  • Fixed "Parameters are not captured inside closures inside closure iterators" (#4070)
  • Fixed "$ For array crashes the compiler when assigned to const" (#4040)
  • Fixed "Default value for .importcpp enum is initialized incorrectly" (#4034)
  • Fixed "Nim doesn't instantiate template parameter in cgen when using procedure return value in for-in loop" (#4110)
  • Fixed "Compile-time SIGSEGV when invoking procedures that cannot be evaluated at compile time from a macro" (#3956)
  • Fixed "Backtricks inside .emit pragma output incorrect name for types" (#3992)
  • Fixed "typedef is generated for .importcpp enums" (#4145)
  • Fixed "Incorrect C code generated for nnkEmpty node" (#950)
  • Fixed "Syntax error in config file appears as general exception without useful info" (#3763)
  • Fixed "Converting .importcpp enum to string doesn't work when done inside procs" (#4147)
  • Fixed "Enum template specifiers do not work for .importcpp enums when they are used as a parameter" (#4146)
  • Fixed "Providing template specifier recursively for .importcpp type doesn't work" (#4148)
  • Fixed "sizeof doesn't work for generics in vm" (#4153)
  • Fixed "Creating list-like structures in a loop leaks memory indefinitely" (#3793)
  • Fixed "Creating list-like structures in a loop leaks memory indefinitely" (#3793)
  • Fixed "Enum items generated by a macro have wrong type." (#4066)
  • Fixed "Memory leak with default GC" (#3184)
  • Fixed "Rationals Overflow Error on 32-bit machine" (#4194)
  • Fixed "osproc waitForExit() is ignoring the timeout parameter" (#4200)
  • Fixed "Regression: exception parseFloat("-0.0") " (#4212)
  • Fixed "JS Codegen: Bad constant initialization order" (#4222)
  • Fixed "Term-rewriting macros gives Error: wrong number of arguments" (#4227)
  • Fixed "importcpp allowed in body of proc after push" (#4225)
  • Fixed "pragma SIGSEGV" (#4001)
  • Fixed "Restrict hints to the current project" (#2159)
  • Fixed "unlikely/likely should be no-ops for the Javascript backend" (#3882)
  • Fixed ".this pragma doesn't work for fields and procs defined for parent type" (#4177)
  • Fixed "VM SIGSEV with compile-time Table" (#3729)
  • Fixed "Error during compilation with cpp option on FreeBSD " (#3059)
  • Fixed "Compiler doesn't keep type bounds" (#1713)
  • Fixed "Stdlib: future: Shortcut proc definition doesn't support, varargs, seqs, arrays, or openarrays" (#4238)
  • Fixed "Why don't asynchttpserver support request-body when put delete?" (#4221)
  • Fixed "Paths for includes in Nim documentation" (#2640)
  • Fixed "Compile pragma doesn't work with relative import" (#1262)
  • Fixed "Slurp doesn't work with relative imports" (#765)
  • Fixed "Make tilde expansion consistent" (#786)
  • Fixed "koch expects nim to be in path for tests?" (#3290)
  • Fixed "Don't use relative imports for non relative modules (aka babel libs)" (#546)
  • Fixed ""echo" on general structs does not work" (#4236)
  • Fixed "Changing math.round() and adding math.integer()" (#3473)
  • Fixed "Mathematics module missing modf" (#4195)
  • Fixed "Passing method to macro causes seg fault" (#1611)
  • Fixed "Internal error with "discard quit"" (#3532)
  • Fixed "SIGSEGV when using object variant in compile time" (#4207)
  • Fixed "formatSize has incorrect prefix" (#4198)
  • Fixed "Add compiler parameter to generate output from source code filters" (#375)
  • Fixed "Add engineering notation to string formatting functions" (#4197)
  • Fixed "Very minor error in json documentation" (#4255)
  • Fixed "can't compile when checking if closure == nil" (#4186)
  • Fixed "Strange code gen for procs returning arrays" (#2259)
  • Fixed "asynchttpserver may consume unbounded memory reading headers" (#3847)
  • Fixed "download page still implies master is default branch" (#4022)
  • Fixed "Use standard compiler flags in build script" (#2128)
  • Fixed "CentOS 6 (gcc-4.4.7) compilation failed (redefinition of typedef)" (#4272)
  • Fixed "doc2 has issues with httpclient" (#4278)
  • Fixed "tuples/tuple_with_nil fails without unsigned module" (#3579)