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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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