[fpc-devel] XML node dump feature

[Ben Grasset]

On Mon, Jun 24, 2019 at 4:11 PM J. Gareth Moreton <gareth at moreton-family.com>
wrote:

> "constexpr" is essentially to C++ as "pure" would be to FPC.  Some of the
> methods that involve pointers and var parameters (which is probably the
> closest equivalent to the "&" parameters in C++) may be flagged as impure
> because they can't be dereferenced at compile time.  Nevertheless, a
> function that simply returns a formatted string, rather than writing
> directly to an output stream, is certainly doable.
>

Well, just to be sure we're on the same page in general, the hypothetical
Pascal equivalent of that program would look something like this I guess:

*program *Example;
*{$mode ObjFPC}
{$modeswitch AdvancedRecords}

**uses *SysUtils;
*type
  generic *TVec3<T> = *record
    *X, Y, Z: T;
    *class function *Create(*const *IX, IY, IZ: T): TVec3; static; pure;
    *class operator *+(constref LHS, RHS: TVec3): TVec3; *vectorcall*; pure;
    *class operator *-(constref LHS, RHS: TVec3): TVec3; *vectorcall*; pure;
    *class operator **(constref LHS, RHS: TVec3): TVec3; *vectorcall*; pure;
    *class operator */(constref LHS, RHS: TVec3): TVec3; *vectorcall*; pure;
    *// This one doesn't really need to be "pure"... normal inlining
would be fine.
    **procedure *Print; pure;
  *end*;

  *class function *TVec3.Create(*const *IX, IY, IZ: T): TVec3;
  *begin
    with *Result *do begin
      *X := IX;
      Y := IY;
      Z := IZ;
    *end*;
  *end*;

  *class operator *TVec3.+(constref LHS, RHS: TVec3): TVec3; *vectorcall*;
  *begin
    *Result := TVec3.Create(LHS.X + RHS.X, LHS.Y + RHS.Y, LHS.Z + RHS.Z);
  *end*;

  *class operator *TVec3.-(constref LHS, RHS: TVec3): TVec3; *vectorcall*;
  *begin
    *Result := TVec3.Create(LHS.X - RHS.X, LHS.Y - RHS.Y, LHS.Z - RHS.Z);
  *end*;

  *class operator *TVec3.*(constref LHS, RHS: TVec3): TVec3; *vectorcall*;
  *begin
    *Result := TVec3.Create(LHS.X * RHS.X, LHS.Y * RHS.Y, LHS.Z * RHS.Z);
  *end*;

  *class operator *TVec3./(constref LHS, RHS: TVec3): TVec3; *vectorcall*;
  *begin
    *Result := TVec3.Create(LHS.X / RHS.X, LHS.Y / RHS.Y, LHS.Z / RHS.Z);
  *end*;

  *procedure *TVec3.Print;
  *begin
    case *GetTypeKind(T) *of
      *tkFloat:
        WriteLn(Format('[%.4f, %.4f, %.4f]', [X, Y, Z]));
      tkInteger, tkInt64, tkQWord:
        WriteLn(Format('[%d, %d, %d]', [X, Y, Z]));
      *otherwise
        *WriteLn('[N/A, N/A, N/A]');
    *end*;
  *end*;
*type *TVec3F = *specialize *TVec3<Single>;
*const
  *A: TVec3F = (X: 1.2; Y: 2.4; Z: 3.8);
  B: TVec3F = (X: 2.1; Y: 4.2; Z: 8.3);
  *// You can't do the next part currently, obviously
  *C: TVec3F = A + B;
  D: TVec3F = A - B;
  E: TVec3F = A * B;
  F: TVec3F = A / B;
*begin
  *C.Print();
  D.Print();
  E.Print();
  F.Print();*end*.
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