Better Software - December 2007 - (Page 11)

Code Craft ATTRIBUTE Compiled (native code) Interpreted Scripting Dynamically Typed Statically Typed Object Oriented Systems Programming Functional Programming Garbage Collection Table 1 LANGUAGES C, C++, D, COBOL, Ada, FORTRAN Java, PHP Perl, C#, Python, JavaScript, Ruby, Lisp, Lua , Perl, Python, JavaScript, Ruby, Lua PHP Perl, Python, JavaScript, Ruby, Lisp, Lua , Java, C, C++, C#, D, COBOL, Ada, FORTRAN All but C (requires modern versions of Ada and FORTRAN) C, C++, D, Ada Lisp (100%), Perl, Python, Ruby, C++, D, Lua Java, PHP Perl, C#, Python, JavaScript, D, Lisp, Lua , (templates) are type-safe. Listing 2 is a simple stack template. Since it is declared with the empty [] syntax, data is a dynamic array. The length property for dynamic arrays can be updated, which resizes the array. Listing 3 is a sample driver for Stack. You use the exclamation point to instantiate a template. Note how the length member function automatically acts as a property in the assert statements (i.e., no function-call syntax is required). Note also that instead of throwing an the features we take for granted in modern programming languages, and then some. The obligatory “Hello, world” program is shown in listing 1. The import statement works just like Java’s, except that modules have a one-to-one correspondence to files, as in Python. // hello.d import std.stdio; void main(string[] args) { writefln("Hello, modern world"); } Listing 1 Free-standing functions behave as in C and C++, except that main doesn’t have to declare int as a return type (although it can). The writef function is like C’s printf with formatting extensions. The writefln function appends a newline. For Java programmers, D has pretty much everything except dynamic class loading, which doesn’t apply since it is a compiled language. Other Java features are there, including interfaces and inner classes. In contrast to Java, D’s generics // stack.d: A stack template struct Stack(T) { private T[] data; public void push(T t) { data ~= t; } public T pop() { T t = data[$-1]; // $ == data.length data.length = data.length-1; return t; } public T top() { return data[$-1]; } public int length() { return data.length; } } Listing 2 import std.stdio; void main() { Stack!(int) s; // Instantiate template s.push(1); assert(s.length == 1); // Property access writefln("top: %d", s.top()); writefln("popping %d", s.pop()); assert(s.length == 0); try { s.top(); // Intentional underflow } catch { writefln("caught exception"); } } /* Output: top: 1 popping 1 caught exception */ Listing 3 public T top() in { assert(data.length > 0); } body { return data[$-1]; } Listing 4 underflow exception in pop and top, I just let automatic array bounds-checking do the job. You could also use D’s built-in support for contract programming to validate preconditions, if you prefer, as the implementation of top in listing 4 illustrates. Preconditions go in an in clause while postconditions go in an out clause. Violated assertions raise an AssertError exception. D can also enforce class invariants. www.StickyMinds.com 11 DECEMBER 2007 BETTER SOFTWARE http://www.StickyMinds.com

Table of Contents Feed for the Digital Edition of Better Software - December 2007

Better Software - December 2007 Contents Mark Your Calendar What's Happening @ StickyMinds.com Technically Speaking Code Craft Test Connection Management Chronicles Man and Machine Let Your Values be Your Guide A Story About User Stories and Test-driven Development Product Announcements The Last Word Ad Index

Better Software - December 2007

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