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Bug 1683227 - Add a note to Maybe::valueOr() about a suboptimal usage. r=sg DONTBUILD

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Differential Revision: https://phabricator.services.mozilla.com/D100071
This commit is contained in:
Ting-Yu Lin 2020-12-21 18:32:26 +00:00
parent 81777ea3b9
commit fd531e4c1a
1 changed files with 7 additions and 0 deletions
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7
mfbt/Maybe.h
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@ -496,6 +496,13 @@ class MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS Maybe
/*
* Returns the contents of this Maybe<T> by value. If |isNothing()|, returns
* the default value provided.
*
* Note: If the value passed to aDefault is not the result of a trivial
* expression, but expensive to evaluate, e.g. |valueOr(ExpensiveFunction())|,
* use |valueOrFrom| instead, e.g.
* |valueOrFrom([arg] { return ExpensiveFunction(arg); })|. This ensures
* that the expensive expression is only evaluated when its result will
* actually be used.
*/
template <typename V>
constexpr T valueOr(V&& aDefault) const {