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| 14 | <div class="section" id="implementing-addition-and"> |
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| 15 | <h1><a class="toc-backref" href="./dimensional-analysis.html#id44" name="implementing-addition-and">Implementing Addition and Subtraction</a></h1> |
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| 16 | <p>We can now easily write the rules for addition and subtraction, |
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| 17 | since the dimensions of the arguments must always match.</p> |
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| 18 | <pre class="literal-block"> |
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| 19 | template <class T, class D> |
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| 20 | quantity<T,D> |
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| 21 | operator+(quantity<T,D> x, quantity<T,D> y) |
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| 22 | { |
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| 23 | return quantity<T,D>(x.value() + y.value()); |
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| 24 | } |
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| 25 | |
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| 26 | template <class T, class D> |
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| 27 | quantity<T,D> |
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| 28 | operator-(quantity<T,D> x, quantity<T,D> y) |
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| 29 | { |
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| 30 | return quantity<T,D>(x.value() - y.value()); |
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| 31 | } |
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| 32 | </pre> |
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| 33 | <!-- @ example.append('void test1() {') # function prologue --> |
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| 34 | <p>These operators enable us to write code like:</p> |
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| 35 | <pre class="literal-block"> |
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| 36 | quantity<float,<strong>length</strong>> len1( 1.0f ); |
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| 37 | quantity<float,<strong>length</strong>> len2( 2.0f ); |
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| 38 | |
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| 39 | len1 = len1 + len2; // OK |
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| 40 | </pre> |
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| 41 | <!-- @litre_translator.line_offset -= 7 --> |
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| 42 | <p>but prevent us from trying to add incompatible dimensions:</p> |
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| 43 | <pre class="literal-block"> |
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| 44 | len1 = len2 + quantity<float,<strong>mass</strong>>( 3.7f ); // <strong>error</strong> |
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| 45 | </pre> |
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| 46 | <!-- @ stack[-1].append('}') # last 2 examples together |
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| 47 | compile('all', pop = 1, expect_error = True) |
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| 48 | |
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| 49 | stack[-1].append('}') # just the prior example |
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| 50 | compile('all', pop = None) --> |
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