On Dec 3, 2009, at 4:15 AM, Sebastian Redl wrote:
> Gabor Greif wrote:
>> Hi all,
>>
>> attached patch simplifies StringSwitch and gets rid of the
>> Copy{Constructible|Assignable} constraint on the type parameter.
>>
> The final conversion still imposes that requirement. Perhaps you should
> change operator T to operator const T&.
FWIW, that will break uses of StringSwitch that try to bind the result to a
temporary, e.g.,
const std::string &R = StringSwitch<std::string>("blarg").Case("blarg",
"temporary");
The temporary std::string built for "temporary" only lives until the end of the
initializer, so R ends up binding to it. I don't know if anyone actually uses
StringSwitch that way, but they're going to get a surprise if they do.
I don't know whether this change actually makes StringSwitch any more
efficient. Did anyone look at the code? We don't care about space efficiency
here, because a single bool on the stack is irrelevant. As for performance,
most string-switches just return an integer or an enum: taking the address of
such things the way stringswitch does is likely to pessimize code. This would
certainly be a win if we did string-switches with heavyweight return types
(like the std::string example above), but I don't know how common that will be.
- Doug
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