Programming in D for Delphi Programmers

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Revision as of 06:15, 4 November 2014 by BBaz (talk | contribs) (Conditional compilation)
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Fundamental syntax changes

Delphi and Pascal comes from another language family than D.

Types equivalence

Pascal D notes
Pointer void*
Byte ubyte 8 bit unsigned integer. note the ambiguity when coming from Pascal.
ShortInt byte 8 bit signed integer
Word uint16 16 bit unsigned integer
SmallInt int16 16 bit signed integer
DWord / Cardinal uint 32 bit unsigned integer
Integer int 32 bit signed integer
UInt64 ulong 64 bit unsigned integer
Int64 long 64 bit signed integer
Single float
Double double
NativeUInt size_t in both case this is either an alias to a unsigned 32 bit integer or to a unsigned 64 bit integer
NativeInt ptrdiff_t in both case this is either an alias to a signed 32 bit integer or to a signed 64 bit integer

The object model

The object model is striclty equivalent. Multiple inherithence of classes is not allowed but can be achieved with interfaces.

Delphi, Pascal

type  ISome = interfaca
    procedure blah();

type TThing = class

type  TSomething = classs(TThing, ISome)
  procedure blah();


interface ISome(){
    void blah();

class TThing{

class TSomething: TThing, ISome{
    void blah(){}


Traditional Delphi and Pascal didn’t supported templates. Delphi supports them since D2009, using the most common syntax: the left/right angle brackets (declaration and instantciation of a template).

D uses parens for the declaration and the ! symbol for the instantiation. Parens are used after the ! if the template expect several parameters.

  • Delphi or FPC with the dialect {$Mode Delphi}
type foo<T,G,A> = class
type fooccc = class(foo<char, char, char>)
  bar: foo<integer,single,double>;
  • FPC with the dialect {$Mode objfpc} (aka modern Pascal)

In the Pascal tradition, the objfpc syntax recquires two explicit keywords for the template declaration and the template instantiation: generic and specialize:

type generic foo<T,G,A> = class

type fooccc = class(specialize foo<char, char, char>)

  bar: specialize foo<integer,single,double>;
  • D
class foo(T,G,A){
alias fooccc = foo!(char, char, char);
foo!(int, float, double) bar;

Conditional compilation

D conditional compilation is one of the unique feature of the lanquage. While in Pascal you used a custom definition like this:

a := a shr 3;
  // some conditionally compiled code

in D the equivalent use a standard language construct version(Identifier):

a =>> 3;
    // some conditionally compiled code   

But now you’ll get more. A feature that doesn’t exist in Pascal and Delphi is the static if expression. It allows a more advanced conditional compilation, particularly in the templates, since it’s allow to test the type of a template parameters when it gets instanciated.

struct foo(T)
    // something is only compiled if T type is string.
    static if (is(T == string)){
    void something(){}

This is also related to the template constraints (the constraint is applied to the whole template while in our previous example it’s only applied to the enclosed expressions). You might know the principle if you’ve used Delphi XE6 or upper.


D has a feature similar to Pascal/delphi source inclusion.

for the example the following inclusion:

procedure Something;

is rewritten in D

void something()
    static enum demoCode = import(myDemoImplementation.d);
    static enum fullCode = import(myFullImplementation.d);
    } else {