[cfe-dev] propagating checker state for duration of a block

[Jordan Rose]

On Dec 17, 2012, at 9:48 , Richard <tarka.t.otter at googlemail.com> wrote:

> well, the idea is to set state if a branch condition is checking for availability, eg
> 
> if ([foo respondsToSelector:@selector(onlyAvailableInIOS6:)]) {
>  // set availability version
>  doIOS6Stuff();
> else {
>  // issue a warning here
>  doIOS6Stuff();
> }
> 
> so a warning can be issued if there is are any methods used newer than the minimum deployment target that are being used without checking for their availability.
> 
> clearly here the state has to be cleared at the end of if {}, otherwise the checker will just assume that all successive calls in the graph have checked for availability already. what would you suggest as a good way of clearing the state once the ifstmt is complete?

Well, no, it doesn't have to be. If I write this:

> if ([foo respondsToSelector:@selector(onlyAvailableInIOS6:)]) {
>   doIOS6Stuff();
> }
> 
> doMoreIOS6Stuff();

The call to 'doMoreIOS6Stuff' will be analyzed twice: once along the true-path from the if-statement, and once along the false-path. So you'd still get a warning on the false path, even though the true path would be quiet. And this is actually what you want for the early return case:

> if (![foo respondsToSelector:@selector(onlyAvailableInIOS6:)])
>   return;
> doIOS6Stuff();


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