在 pascal define 中传递参数

Question

我正在尝试用 pascal (freepascal) 定义一些东西。与在 C++ 中一样，您可以像这样传递变量定义宏：

#define REP(i,k) for(int i=0; i<k; i++)

你如何用 Pascal 实现？

我在第一行添加了{$MACRO ON}命令，结果它可以运行正常定义而没有错误，如{$define lala:='hello world'}。

但是当我尝试 {define lala(i):=i} 程序出现错误。

如何在 Pascal define 中传递可变参数？

Answer 1

使用外部预处理器，并在对结果使用 Pascal 编译器之前在构建系统中执行它。

FPC 宏系统不是用于元编程，而是用于在 headers 中调用约定宏，仅用于压缩 enable/disable 逻辑（如 home-brewn 断言和其他调试日志代码）和不支持参数化。

非 hygienic 宏与 Pascal 单位系统根本不兼容，而 hygienic 宏被内联覆盖 function/procedures。

Answer 2

您可以结合使用宏和包含来实现类似于标记粘贴的效果...

ACME_Integer.inc

const ACME_1 = ACME_3;
const ACME_2 = pred(1 shl ACME_1);
type  ACME_0 = 0..ACME_2;
//clear the passed in parameters so they can be reused in the next inclusion
{$undef ACME_0}{$undef ACME_1}{$undef ACME_2}{$undef ACME_3}

somefile.pas

{$macro on}

{$define  ACME_0:=TAllocationPatchIndex}
{$define  ACME_1:=TAllocationPatchIndex_bits}
{$define  ACME_2:=TAllocationPatchIndex_high}
{$define  ACME_3:=16}
{$Include ACME_Integer.inc} 

{$define  ACME_0:=TAllocationId}
{$define  ACME_1:=TAllocationId_bits}
{$define  ACME_2:=TAllocationId_high}
{$define  ACME_3:=28}
{$Include ACME_Integer.inc}

扩展到

const TAllocationPatchIndex_bits = 16;
const TAllocationPatchIndex_high = pred(1 shl TAllocationPatchIndex_bits);
type  TAllocationPatchIndex= 0..TAllocationPatchIndex_high;

const TAllocationId_bits = 28;
const TAllocationId_high = pred(1 shl TAllocationId_bits);
type  TAllocationId= 0..TAllocationId_high;

虽然此示例使用的代码多于它节省的代码，但您可以明显地看到包含文件可能非常复杂，需要多次自定义的重复代码。

更新 - 使用 named/optional 个参数的更复杂的宏

ACME_Integer.inc

     {$ifdef ACME_packed_array}
         {$undef ACME_array}
         {$define ACME_array:=ACME_packed_array}

         {$undef ACME_array_decl}
         {$define ACME_array_decl:=packed array}
     {$else}

          {$ifdef ACME_bitpacked_array}

             {$undef ACME_array}
             {$define ACME_array:=ACME_bitpacked_array}

             {$undef ACME_array_decl}
             {$define ACME_array_decl:=bitpacked array}

           {$else}
               {$undef ACME_array_decl}
               {$define ACME_array_decl:=array}
           {$endif}
     {$endif}

     {$ifndef ACME_array_type}
         {$define ACME_array_type:=byte}
     {$endif}

     {$ifdef ACME_bitconst}
        // we want to keep the X_bits constant
        const ACME_bitconst = ACME_bits; //X_bits
        {$ifdef ACME_high}
        // we want to keep the X_high constant
        const ACME_high = pred(1 shl ACME_bitconst);    //X_high
        type  ACME_type = 0..ACME_high;             //X
        {$else}
        // we don't care about keeping the X_high constant
        type  ACME_type = 0..pred(1 shl ACME_bitconst); //X
        {$endif}
    {$else}
       {$ifdef ACME_high}
          // we don't care about keeping the X_bits constant
          const ACME_high = pred(1 shl ACME_bits); //X_high
          type  ACME_type = 0..ACME_high;          //X
       {$else}
          // we don't care about keeping the X_high or X_bits constants
          type  ACME_type = 0..pred(1 shl ACME_bits); //X
       {$endif}
    {$endif}

    {$ifdef ACME_array}



      type  ACME_array = ACME_array_decl [ACME_type] of ACME_array_type;

      {$ifdef ACME_array_length}
          const ACME_array_length = sizeof(ACME_array);
      {$endif}


      {$ifdef ACME_array_pointer}
        type  ACME_array_pointer=^ACME_array;
      {$endif}

      {$undef ACME_array}
    {$endif}

{$undef ACME_type}
{$undef ACME_bitconst}
{$undef ACME_high}
{$undef ACME_bits}
{$undef ACME_packed_array}
{$undef ACME_bitpacked_array}
{$undef ACME_array}
{$undef ACME_array_pointer}
{$undef ACME_array_type}
{$undef ACME_array_decl}
{$undef ACME_array_length}

somefile.pas

{$macro on}

{$define  ACME_type:=TSha256IndexSliceMagic}
{$define  ACME_bitconst:=TSha256IndexSliceMagic_bits}
{$define  ACME_high:=TSha256IndexSliceMagic_high}
{$define  ACME_bits:=17}
{$Include ACME_Integer.inc}

{$define  ACME_type:=TSha256DataBufferIndex}
{$define  ACME_bitconst:=TSha256DataBufferIndex_bits}
{$define  ACME_high:=TSha256DataBufferIndex_high}
{$define  ACME_bits:=9}
{$define  ACME_packed_array:=TSha256DataBuffer}
{$define  ACME_array_pointer:=PSha256DataBuffer}
{$Include ACME_Integer.inc}

扩展到

const TSha256IndexSliceMagic_bits = 17;
const TSha256IndexSliceMagic_high = pred(1 shl TSha256IndexSliceMagic_bits);  
type  TSha256IndexSliceMagic= 0..TSha256IndexSliceMagic_high;


const TSha256DataBufferIndex_bits = 9;
const TSha256DataBufferIndex_high = pred(1 shl TSha256DataBufferIndex_bits);  
type  TSha256DataBufferIndex= 0..TSha256DataBufferIndex_high;
type  TSha256DataBuffer = packed array [TSha256DataBufferIndex] of byte;
type  PSha256DataBuffer = ^TSha256DataBuffer;

在 pascal define 中传递参数

Pass parameter in pascal define

macros

pascal

freepascal

preprocessor