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Merged F.40 into F.15 (issue #1

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hsutter
2015-12-01 08:25:56 -08:00
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CppCoreGuidelines.md
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@@ -1790,7 +1790,6 @@ Argument passing rules:
Value return rules: Value return rules:
* [F.40: Prefer return values to out-parameters](#Rf-T-return)
* [F.41: Prefer to return tuples or structs instead of multiple out-parameters](#Rf-T-multi) * [F.41: Prefer to return tuples or structs instead of multiple out-parameters](#Rf-T-multi)
* [F.42: Return a `T*` to indicate a position (only)](#Rf-return-ptr) * [F.42: Return a `T*` to indicate a position (only)](#Rf-return-ptr)
* [F.43: Never (directly or indirectly) return a pointer to a local object](#Rf-dangle) * [F.43: Never (directly or indirectly) return a pointer to a local object](#Rf-dangle)
@@ -2193,7 +2192,7 @@ If you really feel the need for an optimization beyond the common techniques, me
![Normal parameter passing table](./param-passing-normal.png "Normal parameter passing") ![Normal parameter passing table](./param-passing-normal.png "Normal parameter passing")
**For an "output-only" value:** Prefer return values to output parameters. **For an "output-only" value:** Prefer return values to output parameters.
This includes large objects like standard containers that use implicit move operations for performance and to avoid explicit memory management. A return value is harder to miss and harder to misuse than a `T&` (an in-out parameter). This includes large objects like standard containers that use implicit move operations for performance and to avoid explicit memory management. A return value is self-documenting, whereas a `&` could be either in-out or out-only and is liable to be misused.
If you have multiple values to return, [use a tuple](#Rf-T-multi) or similar multi-member type. If you have multiple values to return, [use a tuple](#Rf-T-multi) or similar multi-member type.
##### Example ##### Example
@@ -2333,6 +2332,7 @@ If you need the notion of an optional value, use a pointer, `std::optional`, or
* Flag all `X&&` parameters (where `X` is not a template type parameter name) where the function body uses them without `std::move`. * Flag all `X&&` parameters (where `X` is not a template type parameter name) where the function body uses them without `std::move`.
* Flag access to moved-from objects. * Flag access to moved-from objects.
* Don't conditionally move from objects * Don't conditionally move from objects
* Flag non-`const` reference parameters that are not read before being written to and are a type that could be cheaply returned; they should be "out" return values.
**See also**: [implicit arguments](#Ri-explicit). **See also**: [implicit arguments](#Ri-explicit).
@@ -2530,24 +2530,6 @@ Note that pervasive use of `shared_ptr` has a cost (atomic operations on the `sh
(Not enforceable) This is a too complex pattern to reliably detect. (Not enforceable) This is a too complex pattern to reliably detect.
### <a name="Rf-T-return"></a> F.40: Prefer return values to out-parameters
##### Reason
It's self-documenting. A `&` parameter could be either in/out or out-only.
##### Example
void incr(int&);
int incr(int);
int i = 0;
incr(i);
i = incr(i);
##### Enforcement
Flag non-`const` reference parameters that are not read before being written to and are a type that could be cheaply returned.
### <a name="Rf-T-multi"></a> F.41: Prefer to return tuples or structs instead of multiple out-parameters ### <a name="Rf-T-multi"></a> F.41: Prefer to return tuples or structs instead of multiple out-parameters