FPC New Features Trunk

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Revision as of 16:12, 20 July 2019 by Jonas (talk | contribs) (Removed FPC 3.2 new features)

About this page

Below you can find a list of new features introduced since the previous release, along with some background information and examples. Note that since svn trunk is by definition still under development, some of the features here may still change before they end up in a release version.

A list of changes that may break existing code can be found here.

All systems


Support for "volatile" intrinsic

  • Overview: A volatile intrinsic has been added to indicate to the code generator that a particular load from or store to a memory location must not be removed.
  • Notes: Delphi uses an attribute rather than an intrinsic. Such support will be added once support for attributes is available in FPC. An intrinsic that applies only to a specific memory access also has the advantages outlined in https://lwn.net/Articles/233482/
  • Example: https://svn.freepascal.org/svn/fpc/trunk/tests/test/tmt1.pp
  • svn: 40465

Support for "noinline" modifier

  • Overview: A noinline modifier has been added that can be used to prevent a routine from ever being inlined (even by automatic inlining).
  • Notes: Mainly added for internal compiler usage related to LLVM support.
  • svn: 41198

Support for multiple active helpers per type

  • Overview: With the modeswitch multihelpers multiple helpers for a single type can be active at once. If a member of the type is accessed it's first checked in all helpers that are in scope in reverse order before the extended type itself is checked.
  • Examples: All tests with the name tmshlp*.pp in https://svn.freepascal.org/svn/fpc/trunk/tests/test
  • svn: 42026

Support for custom attributes

  • Overview: Custom attributes allow to decorate types and published properties of classes to be decorated with additional metadata. The metadata are by itself descendants of TCustomAttribute and can take additional parameters if the classes have a suitable constructor to take these parameters. This feature requires the new modeswitch PrefixedAttributes. This modeswitch is active by default in modes Delphi and DelphiUnicode. Attributes can be queried using the TypInfo or Rtti units.
  • Notes: More information can be seen in the announcement mail and Custom Attributes
  • svn: 42356 - 42411
  • Example:
program tcustomattr;

{$mode objfpc}{$H+}
{$modeswitch prefixedattributes}

  TMyAttribute = class(TCustomAttribute)
    constructor Create;
    constructor Create(aArg: String);
    constructor Create(aArg: TGUID);
    constructor Create(aArg: LongInt);

  TTestClass = class
    fTest: LongInt;
    property Test: LongInt read fTest;

  [TMy('Hello World')]
  TTestEnum = (

  [TMyAttribute(IInterface), TMy(42)]
  TLongInt = type LongInt;

constructor TMyAttribute.Create;

constructor TMyAttribute.Create(aArg: String);

constructor TMyAttribute.Create(aArg: LongInt);

constructor TMyAttribute.Create(aArg: TGUID);




Registry unit

  • Overview: The TRegistry class was made to be fully Unicode capable.
  • Notes:
    • All public and protected methods (the public API) that used string parameters now default to use UnicodeString parameters.
    • For all these methods overloads exist using String parameters (these call their UnicodeString counterparts).
    • Methods using TStrings have counterparts using TUnicodeStringArray, and ReadStringList/WriteStringList let you specify if the TStrings should be treated as UTF8 encoded.
    • The public API of TXMLRegistry was changed to use UnicodeString everywhere, without having String overloads. TXMLRegistry interfaces with a TXMLDocument structure internally, which uses DOMString (which in turn is an alias to WideString).
    • TRegIniFile and TRegistryIniFile have been deprecated on non-Windows platforms.
    • The public API of TRegIniFile has not been changed.
  • More information: https://lists.freepascal.org/pipermail/fpc-devel/2019-February/040446.html
  • svn: r41784

New compiler targets

Support for code generation through LLVM

  • Overview: The compiler now has a code generator that generates LLVM bitcode.
  • Notes: LLVM still requires target-specific support and modifications in the compiler. Initially, the LLVM code generator only works when targeting Darwin/x86-64, Linux/x86-64, Linux/ARMHF and Linux/AArch64.
  • More information: LLVM
  • svn: 42260

New Features from other versions