Comparison

To D, or not to D.

William Nerdspeare

This table is a quick and rough list of various features of D that can be used to compare with other languages. While many capabilities are available with standard libraries, this table is for features built in to the core language itself. Rationale.

Notes

Object Oriented

This means support for classes, member functions, inheritance, and virtual function dispatch.

Inline assembler

Many C and C++ compilers support an inline assembler, but this is not a standard part of the language, and implementations vary widely in syntax and quality.

Interfaces

Support in C++ for interfaces is weak enough that an IDL (Interface Description Language) was invented to compensate.

Modules

Many correctly argue that C++ doesn't really have modules. But C++ namespaces coupled with header files share many features with modules.

Garbage Collection

The Hans-Boehm garbage collector can be successfully used with C and C++, but it is not a standard part of the language.

Implicit Type Inference

This refers to the ability to pick up the type of a declaration from its initializer.

Contract Programming

The Digital Mars C++ compiler supports Contract Programming as an extension. Compare some C++ techniques for doing Contract Programming with D.

Resizeable arrays

Part of the standard library for C++ implements resizeable arrays, however, they are not part of the core language. A conforming freestanding implementation of C++ (C++98 17.4.1.3) does not need to provide these libraries.

Built-in Strings

Part of the standard library for C++ implements strings, however, they are not part of the core language. A conforming freestanding implementation of C++ (C++98 17.4.1.3) does not need to provide these libraries.

Use existing debuggers

By this is meant using common debuggers that can operate using debug data in common formats embedded in the executable. A specialized debugger useful only with that language is not required.

Struct member alignment control

Although many C/C++ compilers contain pragmas to specify struct alignment, these are nonstandard and incompatible from compiler to compiler.
The C# standard ECMA-334 25.5.8 says only this about struct member alignment: "The order in which members are packed into a struct is unspecified. For alignment purposes, there may be unnamed padding at the beginning of a struct, within a struct, and at the end of the struct. The contents of the bits used as padding are indeterminate." Therefore, although Microsoft may have extensions to support specific member alignment, they are not an official part of standard C#.

Support all C types

C99 adds many new types not supported by C++.

80 bit floating point

While the standards for C and C++ specify long doubles, few compilers (besides Digital Mars C/C++) actually implement 80 bit (or longer) floating point types.

Mixins

Mixins have many different meanings in different programming languages. D mixins mean taking an arbitrary sequence of declarations and inserting (mixing) them into the current scope. Mixins can be done at the global, class, struct, or local level.

C++ Mixins

C++ mixins refer to a couple different techniques. The first is analogous to D's interface classes. The second is to create a template of the form:

template <class Base> class Mixin : public Base
{
    ... mixin body ...
}

D mixins are different.

Static If

The C and C++ preprocessor directive #if would appear to be equivalent to the D static if. But there are major and crucial differences - the #if does not have access to any of the constants, types, or symbols of the program. It can only access preprocessor macros. See this example.

Is Expressions

Is expressions enable conditional compilation based on the characteristics of a type. This is done after a fashion in C++ using template parameter pattern matching. See this example for a comparison of the different approaches.

Inner (adaptor) classes

A nested class is one whose definition is within the scope of another class. An inner class is a nested class that can also reference the members and fields of the lexically enclosing class; one can think of it as if it contained a 'this' pointer to the enclosing class.

Documentation comments

Documentation comments refer to a standardized way to produce documentation from the source code file using specialized comments.