Container Algorithms

On the other hand, I always worry about all the magic implicit behavior in C++, both in old and new language features. We're writing in C++, we care about efficiency. Eric addresses this by requiring rvalue references in the container algorithms, but in general it's pretty easy to write code that does more work than you expected.

Since most undesired magic in C++ boils down to allocating heap memory unexpectedly, it would be cool to add syntax to could tell the compiler that a block is not allowed to allocate, like:

    noalloc {
        bigvec = std::move(bigvec) | cont::sort | cont::unique;
    }

Why can't the

    std::vector<int> ints =
        read_ints() | cont::sort | cont::unique;

    std::vector<int> ints(read_ints() | cont::sort | cont::unique);

    std::vector<int> ints;
    read_ints() | cont::sort | cont::unique > ints;

Performance-wise, the lazy filter works in constant space, will result in fewer dcache misses if the data set is large, and (I think) provides more opportunity for the optimizer to do clever things. The eager chain may have better icache performance if the filter is very complicated.

And it's easy to go from lazy to eager -- just put everything in a vector. If you want to go from eager to lazy, though, you're out of luck.