use of string_view in as<T> method #1187
Conversation
| @@ -319,7 +319,7 @@ class Option : public OptionBase<Option> { | |||
| /// complete Results of parsing | |||
| results_t results_{}; | |||
| /// results after reduction | |||
| results_t proc_results_{}; | |||
| mutable results_t proc_results_{}; | |||
There was a problem hiding this comment.
Why mutable? Generally that means this is thread safe, while results_t won't necessarily be thread safe?
There was a problem hiding this comment.
The key issue is the results and related as<T> method. These methods are const as normally they should not result in changes to the data structure. This converts the results to whatever is requested. But in cases where the results are requested as a string_view and there was no data given in the parsing, and there was a default value given. This can lead to undefined behavior in the way we were doing it, as the string_view could end up pointing to a temporary. Some compilers handled this gracefully others didn't. The simplest lowest impact solution to this was to make proc_results which is where processed results are stored in the mutable object so it can be modified in a const method in those few select cases and prevent undefined behavior. The other options were to just ban string_view but would not solve the underlying problem, just the most common exemplar of it. Make some more complicated storage buffers, or force processing for all options to pre fill the results structures. My assessment was that this was the least intrusive and simplest option.
Address Issue #881, allowing use of string_view in the as method on options.