The following articles provide an introduction to Design by Contract.

Design by Contract (Wikipedia)

IContract (Java Implementation)

Building bug-free O-O software: An introduction to Design by Contract (In the Eiffel)

ColdContract now has a project at RIAForge.org http://coldcontract.riaforge.org/.

You’ll have to download it form the SVN repo for now, as there is not realy anything worth packageing up for download yet

I have been playing around with implementing Design by Contract in ColdFusion using Coldspring's AOP functionality.

ColdContract is a Coldspring AOP Advice which allows Design by Contract assertions to be added to ColdFusion components and for those assertions to be executed during program execution.

Design by Contract assertions are a mechanism for defining the specification of software components, in such a way as to allow the implementation of the specification to be tested in-line with program execution. This provides a difference (and arguably quicker) method of implementing TDD to Unit Testing.

Assertions are added to components using meta data attributes as shown below:

1. <!---


2. /**
3. *
4. * Copyright (c) 2008 David Beale (http://www.BealeARTS.co.uk)
5. *
6. **/
7. --->
8.  
9. <cfcomponent displayname="Stack"

10. hint="A FILO Stack example showing the use of ColdContract assertions. Stack items cannot be objects (Components)."
11. invariants="this.getNumberOfItems() gte 0, this.getNumberOfItems() eq arrayLen(variables.stack)"
12. >
13.  
14. <!--- INIT --->
15.  
16. <cffunction name="init"

17. hint="Constructor"
18. access="public"
19. returnType="Stack"
20. output="false"
21. >
22. <cfreturn this />
23. </cffunction>
24.  
25.  
26. <!--- PUBLIC --->
27.  
28. <cffunction name="push"

29. hint="Push an item onto the stack"
30. access="public"
31. returnType="void"
32. output="false"
33. preconditions="not isObject(arguments.item)"
34. postconditions="this.getNumberOfItems() eq oldThis.getNumberOfItems() + 1"
35. >
36. <cfargument name="item" hint="Item to add" type="any" required="true" />
37.  
38. <cfset arrayAppend(variables.stack, arguments.item) />
39. <cfset variables.stackIndex++ />
40.  
41. </cffunction>
42.  
43.  
44. <cffunction name="pop"

45. hint="Pop an item off the stack"
46. access="public"
47. returnType="any"
48. output="false"
49. preconditions="this.getNumberOfItems() gt 0"
50. postconditions="this.getNumberOfItems() eq oldThis.getNumberOfItems() - 1, not isObject(cfreturn)"
51. >
52.  
53. <!--- LOCALS --->
54. <cfset item = '' />
55.  
56. <cfset item = variables.stack[variables.stackIndex] />
57. <cfset arrayDeleteAt(variables.stack, variables.stackIndex) />
58. <cfset variables.stackIndex-- />
59.  
60. <cfreturn item />
61. </cffunction>
62.  
63.  
64. <cffunction name="getNumberOfItems"

65. hint="Get the number of items on the stack"
66. access="public"
67. returnType="numeric"
68. output="false"
69. >
70. <cfreturn arrayLen(variables.stack) />
71. </cffunction>
72.  
73.  
74. <!--- PRIVATE --->
75.  
76. <cfset variables.stack = arrayNew(1) />
77.  
78. <cfset variables.stackIndex = 0 />
79.  
80. </cfcomponent>
81. Download this code: stack.cfc