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v1.8.x - yyyy-mm-dd

Changes affecting backward compatibility

  • addr is now available for all addressable locations, unsafeAddr is now deprecated and an alias for addr.

  • io, assertions, formatfloat, and dollars.`$` for objects are about to move out of the system module. You may instead import std/syncio, std/assertions, std/formatfloat and std/objectdollar. The -d:nimPreviewSlimSystem option makes these imports required.

  • The gc:v2 option is removed.

  • The mainmodule and m options are removed.

  • The threads:on option is now the default.

  • Optional parameters in combination with : body syntax (RFC #405) are now opt-in via experimental:flexibleOptionalParams.

Standard library additions and changes

  • Pointer to cstring conversion now triggers a [PtrToCstringConv] warning. This warning will become an error in future versions! Use a cast operation like cast[cstring](x) instead.

  • logging will default to flushing all log level messages. To get the legacy behaviour of only flushing Error and Fatal messages, use -d:nimV1LogFlushBehavior.

  • Object fields now support default values, see https://nim-lang.github.io/Nim/manual.html#types-default-values-for-object-fields for details.

  • Redefining templates with the same signature was previously allowed to support certain macro code. To do this explicitly, the {.redefine.} pragma has been added. Note that this is only for templates. Implicit redefinition of templates is now deprecated and will give an error in the future.

  • Using an unnamed break in a block is deprecated. This warning will become an error in future versions! Use a named block with a named break instead.

  • Several Standard libraries are moved to nimble packages, use nimble to install them:

    • std/punycode => punycode
    • std/asyncftpclient => asyncftpclient
    • std/smtp => smtp
    • std/db_common => db_connector/db_common
    • std/db_sqlite => db_connector/db_sqlite
    • std/db_mysql => db_connector/db_mysql
    • std/db_postgres => db_connector/db_postgres
    • std/db_odbc => db_connector/db_odbc

  • Previously, calls like foo(a, b): ... or foo(a, b) do: ... where the final argument of foo had type proc () were assumed by the compiler to mean foo(a, b, proc () = ...). This behavior is now deprecated. Use foo(a, b) do (): ... or foo(a, b, proc () = ...) instead.

  • If no exception or any exception deriving from Exception but not Defect or CatchableError given in except, a warnBareExcept warning will be triggered.

Standard library additions and changes

  • macros.parseExpr and macros.parseStmt now accept an optional filename argument for more informative errors.
  • Module colors expanded with missing colors from the CSS color standard.
  • Fixed lists.SinglyLinkedList being broken after removing the last node (#19353).

Language changes

  • Pragma macros on type definitions can now return nnkTypeSection nodes as well as nnkTypeDef, allowing multiple type definitions to be injected in place of the original type definition.

    import macros

macro multiply(amount: static int, s: untyped): untyped =
  let name = $s[0].basename
  result = newNimNode(nnkTypeSection)
  for i in 1 .. amount:
    result.add(newTree(nnkTypeDef, ident(name & $i), s[1], s[2]))

type
  Foo = object
  Bar {.multiply: 3.} = object
    x, y, z: int
  Baz = object

# becomes

type
  Foo = object
  Bar1 = object
    x, y, z: int
  Bar2 = object
    x, y, z: int
  Bar3 = object
    x, y, z: int
  Baz = object

  • Case statement macros are no longer experimental, meaning you no longer need to enable the experimental switch caseStmtMacros to use them.

Compiler changes

  • nim can now compile version 1.4.0 as follows: nim c --lib:lib --stylecheck:off compiler/nim, without requiring -d:nimVersion140 which is now a noop.

  • --styleCheck, --hintAsError and --warningAsError now only applies to the current package.

Tool changes

  • The gc switch has been renamed to mm ("memory management") in order to reflect the reality better. (Nim moved away from all techniques based on "tracing".)

  • Nim now supports Nimble version 0.14 which added support for lock-files. This is done by a simple configuration change setting that you can do yourself too. In $nim/config/nim.cfg replace pkgs by pkgs2.

  • There is a new switch --nimMainPrefix:prefix to influence the NimMain that the compiler produces. This is particularly useful for generating static libraries.