| 1 | <?xml version="1.0" encoding="utf-8" ?> |
|---|
| 2 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> |
|---|
| 3 | <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> |
|---|
| 4 | <!-- Copyright Aleksey Gurtovoy 2006. Distributed under the Boost --> |
|---|
| 5 | <!-- Software License, Version 1.0. (See accompanying --> |
|---|
| 6 | <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> |
|---|
| 7 | <head> |
|---|
| 8 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> |
|---|
| 9 | <meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" /> |
|---|
| 10 | <title>THE BOOST MPL LIBRARY: Implementing Addition and Subtraction</title> |
|---|
| 11 | <link rel="stylesheet" href="../style.css" type="text/css" /> |
|---|
| 12 | </head> |
|---|
| 13 | <body class="docframe"> |
|---|
| 14 | <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./representing-quantities.html" class="navigation-link">Prev</a> <a href="./implementing.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./representing-quantities.html" class="navigation-link">Back</a> <a href="./implementing.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./dimensional-analysis.html" class="navigation-link">Up</a> <a href="../index.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./tutorial_toc.html" class="navigation-link">Full TOC</a></span></td> |
|---|
| 15 | <td class="header-group page-location"><a href="../index.html" class="navigation-link">Front Page</a> / <a href="./tutorial-metafunctions.html" class="navigation-link">Tutorial: Metafunctions and Higher-Order Metaprogramming</a> / <a href="./dimensional-analysis.html" class="navigation-link">Dimensional Analysis</a> / <a href="./implementing-addition-and.html" class="navigation-link">Implementing Addition and Subtraction</a></td> |
|---|
| 16 | </tr></table><div class="header-separator"></div> |
|---|
| 17 | <div class="section" id="implementing-addition-and"> |
|---|
| 18 | <h1><a class="toc-backref" href="./dimensional-analysis.html#id44" name="implementing-addition-and">Implementing Addition and Subtraction</a></h1> |
|---|
| 19 | <p>We can now easily write the rules for addition and subtraction, |
|---|
| 20 | since the dimensions of the arguments must always match.</p> |
|---|
| 21 | <pre class="literal-block"> |
|---|
| 22 | template <class T, class D> |
|---|
| 23 | quantity<T,D> |
|---|
| 24 | operator+(quantity<T,D> x, quantity<T,D> y) |
|---|
| 25 | { |
|---|
| 26 | return quantity<T,D>(x.value() + y.value()); |
|---|
| 27 | } |
|---|
| 28 | |
|---|
| 29 | template <class T, class D> |
|---|
| 30 | quantity<T,D> |
|---|
| 31 | operator-(quantity<T,D> x, quantity<T,D> y) |
|---|
| 32 | { |
|---|
| 33 | return quantity<T,D>(x.value() - y.value()); |
|---|
| 34 | } |
|---|
| 35 | </pre> |
|---|
| 36 | <!-- @ example.append('void test1() {') # function prologue --> |
|---|
| 37 | <p>These operators enable us to write code like:</p> |
|---|
| 38 | <pre class="literal-block"> |
|---|
| 39 | quantity<float,<strong>length</strong>> len1( 1.0f ); |
|---|
| 40 | quantity<float,<strong>length</strong>> len2( 2.0f ); |
|---|
| 41 | |
|---|
| 42 | len1 = len1 + len2; // OK |
|---|
| 43 | </pre> |
|---|
| 44 | <!-- @litre_translator.line_offset -= 7 --> |
|---|
| 45 | <p>but prevent us from trying to add incompatible dimensions:</p> |
|---|
| 46 | <pre class="literal-block"> |
|---|
| 47 | len1 = len2 + quantity<float,<strong>mass</strong>>( 3.7f ); // <strong>error</strong> |
|---|
| 48 | </pre> |
|---|
| 49 | <!-- @ stack[-1].append('}') # last 2 examples together |
|---|
| 50 | compile('all', pop = 1, expect_error = True) |
|---|
| 51 | |
|---|
| 52 | stack[-1].append('}') # just the prior example |
|---|
| 53 | compile('all', pop = None) --> |
|---|
| 54 | </div> |
|---|
| 55 | |
|---|
| 56 | <div class="footer-separator"></div> |
|---|
| 57 | <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./representing-quantities.html" class="navigation-link">Prev</a> <a href="./implementing.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./representing-quantities.html" class="navigation-link">Back</a> <a href="./implementing.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./dimensional-analysis.html" class="navigation-link">Up</a> <a href="../index.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./tutorial_toc.html" class="navigation-link">Full TOC</a></span></td> |
|---|
| 58 | </tr></table></body> |
|---|
| 59 | </html> |
|---|
