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add example to F.21

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Bjarne Stroustrup
2017-04-02 20:39:55 -04:00
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CppCoreGuidelines.md
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@@ -1,6 +1,6 @@
# <a name="main"></a>C++ Core Guidelines # <a name="main"></a>C++ Core Guidelines
March 27, 2017 April 2, 2017
Editors: Editors:
@@ -2902,7 +2902,15 @@ However, we prefer to be explicit, rather than subtle.
In many cases, it may be useful to return a specific, user-defined "Value or error" type. In many cases, it may be useful to return a specific, user-defined "Value or error" type.
For example: For example:
struct struct Distance {
int value;
int unit = 1; // 1 mens meters
};
Distance d1 = measure(obj1); // access d1.value and d1.unit
auto d2 = measure(obj2); // access d2.value and d2.unit
auto [value, unit] = measure(obj3); // access value and unit; somewhat redundant to people who know measure()
auto [x,y] = measure(obj4); // don't; it's likely to be confusiong
The overly-generic `pair` and `tuple` should be used only when the value returned represents to independent entities rather than an abstraction. The overly-generic `pair` and `tuple` should be used only when the value returned represents to independent entities rather than an abstraction.