Cover fe ature 47 january 2012 Published by the ieee computer Society 0018-9162/12/$31. 00 2012 ieee

Figure 1. 

List versus vector timings.

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COVER FE ATURE

compUteR

 

52

information is encoded in the type system.

Consider

void increase_to(double speed);  

// speed in m/s

This is an error waiting to happen. Maybe we understand 

the requirements for an argument, but they only appear in 

comments and other documentation. Is 

increase_to(7.2)

 

correct? Does 

7.2

 represent a speed? If so, in what units? 

A better try would be

void increase_to(Speed s);

Given a reasonable definition of 

Speed

, 

increase_to(7.2)

 

is an error and 

increase_to(72m/10s)

 is likely to be cor-

rect. This isn’t just an issue of units; I have a philosophical 

problem with parameters of near-universal types. For 

example, an integer can represent just about everything. 

Consider

// construct a rectangle: