Question

I was exploring C++0x today, and I encountered the new lambda feature. My question is how are these different (in terms of use) from blocks and why might one prefer one over the other?

Thanks.

Answer 1

there is a a short syntax with C++0x lambdas to take every variable in
scope by reference. ([&]) The type of a lambda is also unspecified,
allowing potentially more optimal code.

Now, when you look at Apple blocks, it will require __block specifiers
added to variables you want to modify (the very fact that this is
required suggests the whole system is defective). Variables are taken
by reference but then by value when the block exits the scope (and the
copied context necessarily lives on the heap, it seems). A weird
semantic that will only lead to broken designs, but probably makes
people that love GC happy. Without saying this probably has quite the
efficiency cost, of course, since this requires special indirections.

It is claimed the C++0x lambdas syntax would break compatibility with
C programs, but I don’t think that is true. There are probably other
problems to integrate it with C, though, mainly the fact that C can’t
really deal with unspecified types and build type erasure.

Apple blocks is really just an ObjC feature they try to generalize to
other languages. For C++, the system designed for that language is
just so much better.

EDIT:

To properly give credit, I took this information from http://www.rhinocerus.net/forum/language-c-moderated/558214-blocks-vs-c-lambdas.html a long time ago. That link is dead now; however, the original discussion appears to be archived here, thanks to @stefan for finding it.