在帕斯卡定义中传递参数

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++)

你怎么能用帕斯卡做到这一点？

我在第一行添加了{$MACRO ON} 命令，因此它可以正常运行define 而不会出现{$define lala:='hello world'} 这样的错误。

但是当我尝试{define lala(i):=i} 时，程序出错了。

如何在 Pascal 定义中传递可变参数？

Answer 1

使用外部预处理器，并在构建系统中执行它，然后再对结果使用 Pascal 编译器。

FPC 宏系统并非用于元编程，而是仅用于调用标头中的约定宏和紧凑的启用/禁用逻辑（如自制断言和其他调试日志记录代码），并且不支持参数化。

非卫生宏与帕斯卡单位系统根本不兼容，卫生宏被内联函数/过程覆盖。

Answer 2

您可以使用宏和包含的组合来实现类似于令牌粘贴的功能...

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节省的代码，但您显然可以看到包含文件可能是相当复杂的重复代码，需要多次自定义。

更新 - 使用命名/可选参数的更复杂的宏

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;