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18 <h1><a class=
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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
>
24 operator+(quantity
<T,D
> x, quantity
<T,D
> y)
26 return quantity
<T,D
>(x.value() + y.value());
29 template
<class T, class D
>
31 operator-(quantity
<T,D
> x, quantity
<T,D
> y)
33 return quantity
<T,D
>(x.value() - y.value());
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 );
42 len1 = len1 + len2; // OK
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>
49 <!-- @ stack[-1].append('}') # last 2 examples together
50 compile('all', pop = 1, expect_error = True)
52 stack[-1].append('}') # just the prior example
53 compile('all', pop = None) -->
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