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Remove claims that "constexpr functions are pure" (#1307)

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F.4 and F.8 made this erroneous claim as parts of notes which are
entirely removed.
This commit is contained in:
Max Bozzi
2019-01-03 14:05:55 -05:00
committed by Herb Sutter
parent 714bec5010
commit dd8fc629d7
1 changed files with 0 additions and 29 deletions
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CppCoreGuidelines.md
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@@ -2601,25 +2601,6 @@ it just guarantees that the function can be evaluated at compile time for consta
##### Note
`constexpr` functions are pure: they can have no side effects.
int dcount = 0;
constexpr int double(int v)
{
++dcount; // error: attempted side effect from constexpr function
return v + v;
}
This is usually a very good thing.
When given a non-constant argument, a `constexpr` function can throw.
If you consider exiting by throwing a side effect, a `constexpr` function isn't completely pure;
if not, this is not an issue.
??? A question for the committee: can a constructor for an exception thrown by a `constexpr` function modify state?
"No" would be a nice answer that matches most practice.
##### Note
Don't try to make all functions `constexpr`.
Most computation is best done at run time.
@@ -2795,16 +2776,6 @@ Pure functions are easier to reason about, sometimes easier to optimize (and eve
template<class T>
auto square(T t) { return t * t; }
##### Note
`constexpr` functions are pure.
When given a non-constant argument, a `constexpr` function can throw.
If you consider exiting by throwing a side effect, a `constexpr` function isn't completely pure;
if not, this is not an issue.
??? A question for the committee: can a constructor for an exception thrown by a `constexpr` function modify state?
"No" would be a nice answer that matches most practice.
##### Enforcement
Not possible.