Nim/changelog.md

v2.x.x - yyyy-mm-dd

Changes affecting backward compatibility

• -d:nimPreviewFloatRoundtrip becomes the default. system.addFloat and system.$ now can produce string representations of floating point numbers that are minimal in size and possess round-trip and correct rounding guarantees (via the Dragonbox algorithm). Use -d:nimLegacySprintf to emulate old behaviors.

• The default parameter of tables.getOrDefault has been renamed to def to avoid conflicts with system.default, so named argument usage for this parameter like getOrDefault(..., default = ...) will have to be changed.

• With -d:nimPreviewCheckedClose, the close function in the std/syncio module now raises an IO exception in case of an error.

• Unknown warnings and hints now gives warnings warnUnknownNotes instead of errors.

• With -d:nimPreviewAsmSemSymbol, backticked symbols are type checked in the asm/emit statements.

• The bare except: now panics on Defect. Use except Exception: or except Defect: to catch Defect. --legacy:noPanicOnExcept is provided for a transition period.

Standard library additions and changes

• setutils.symmetricDifference along with its operator version setutils.`-+-` and in-place version setutils.toggle have been added to more efficiently calculate the symmetric difference of bitsets.
• strutils.multiReplace overload for character set replacements in a single pass. Useful for string sanitation. Follows existing multiReplace semantics.

• std/math The ^ symbol now supports floating-point as exponent in addition to the Natural type.

• system.substr implementation now uses copymem (wrapped C memcpy) for copying data, if available at compilation.

• system.newStringUninit is now considered free of side-effects allowing it to be used with --experimental:strictFuncs.

Language changes

• An experimental option --experimental:typeBoundOps has been added that implements the RFC https://github.com/nim-lang/RFCs/issues/380. This makes the behavior of interfaces like hash, $, == etc. more reliable for nominal types across indirect/restricted imports.

  # objs.nim
  import std/hashes
  
  type
    Obj* = object
      x*, y*: int
      z*: string # to be ignored for equality
  
  proc `==`*(a, b: Obj): bool =
    a.x == b.x and a.y == b.y
  
  proc hash*(a: Obj): Hash =
    $!(hash(a.x) &! hash(a.y))
  

  # main.nim
  {.experimental: "typeBoundOps".}
  from objs import Obj # objs.hash, objs.`==` not imported
  import std/tables
  
  var t: Table[Obj, int]
  t[Obj(x: 3, y: 4, z: "debug")] = 34
  echo t[Obj(x: 3, y: 4, z: "ignored")] # 34
  

  See the experimental manual for more information.

Compiler changes

Tool changes

• Added --stdinfile flag to name of the file used when running program from stdin (defaults to stdinfile.nim)