The second major feature of Blocks vs c++ lambdas is that they can be
"copied onto the heap". This allows things like "Grand Central Dispatch"
to work: you can write code that executes blocks asynchronously or on
other threads/work queues (after the function containing the block has
returned). A simple example is:
void print_on_different_thread(int X) {
run_asynch(^{
printf("Hi %d\n", X);
});
}
With lambdas, the closure would be go out of scope when
print_on_different_thread returns, but blocks allows "run_asynch" to
extend the lifetime of the block.