Component programming

[Chris]

This is only losely related to D, but I don't fully understand 
the separation of component programming and OOP (cf. 
https://en.wikipedia.org/wiki/Component-based_software_engineering#Differences_from_object-oriented_programming). 
In an OO framwork, the objects are basically components. See also

"Brad Cox of Stepstone largely defined the modern concept of a 
software component.[4] He called them Software ICs and set out to 
create an infrastructure and market for these components by 
inventing the Objective-C programming language." (see link above)

Walter's example 
(http://www.drdobbs.com/architecture-and-design/component-programming-in-d/240008321)

void main() {
         stdin.byLine(KeepTerminator.yes)    // 1
         map!(a => a.idup).                  // 2
         array.                              // 3
         sort.                               // 4
         copy(                               // 5
             stdout.lockingTextWriter());    // 6
     }

This is more or less how mature OO programs look like. Ideally 
each class (component) does one thing (however small the class 
might be) and can be used or called to perform this task. All 
other classes or components can live independently. From my 
experience this is exactly what Objective-C does. Rather than 
subclassing, it uses other classes to get a job done.