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| <div class="section" id="implementing-addition-and"> |
| <h1><a class="toc-backref" href="./dimensional-analysis.html#id44" name="implementing-addition-and">Implementing Addition and Subtraction</a></h1> |
| <p>We can now easily write the rules for addition and subtraction, |
| since the dimensions of the arguments must always match.</p> |
| <pre class="literal-block"> |
| template <class T, class D> |
| quantity<T,D> |
| operator+(quantity<T,D> x, quantity<T,D> y) |
| { |
| return quantity<T,D>(x.value() + y.value()); |
| } |
| |
| template <class T, class D> |
| quantity<T,D> |
| operator-(quantity<T,D> x, quantity<T,D> y) |
| { |
| return quantity<T,D>(x.value() - y.value()); |
| } |
| </pre> |
| <!-- @ example.append('void test1() {') # function prologue --> |
| <p>These operators enable us to write code like:</p> |
| <pre class="literal-block"> |
| quantity<float,<strong>length</strong>> len1( 1.0f ); |
| quantity<float,<strong>length</strong>> len2( 2.0f ); |
| |
| len1 = len1 + len2; // OK |
| </pre> |
| <!-- @litre_translator.line_offset -= 7 --> |
| <p>but prevent us from trying to add incompatible dimensions:</p> |
| <pre class="literal-block"> |
| len1 = len2 + quantity<float,<strong>mass</strong>>( 3.7f ); // <strong>error</strong> |
| </pre> |
| <!-- @ stack[-1].append('}') # last 2 examples together |
| compile('all', pop = 1, expect_error = True) |
| |
| stack[-1].append('}') # just the prior example |
| compile('all', pop = None) --> |
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