Open Radar

 
Currently there appears to be no secure way to check blocks for validity, other than
    [block isKindOfClass:NSClassFromString(@"NSBlock")].

Further more the lack of a public protocol/class makes it hard (if not impossible) to safely accept a block as a method argument. You have to check at runtime using said (hacky-ish) method call (see above).

If exposing NSBlock to the public is a no-go for Apple (for reasony of internal implementation, or whatever), then please at least provide a public tagging protocol for blocks!

This way one could exchange
    [block isKindOfClass:NSClassFromString(@"NSBlock")].
for a much safer
    [block conformsToProtocol:@protocol(NSBlock)].

One could also have it throw compile time errors when using blocks as arguments.

    @protocol NSBlock
    //empty method list
    @end

    @interface NSBlock <NSBlock> {…}
    //existing private interface
    @end