Parallel Merge Sort

[Josh via Digitalmars-d]

> Bye,
> bearophile

My problem is understanding the syntax. I'm coming from 
Java/C++/Rust so it's not a huge stretch for me.
Would you mind explaining the major syntax in this piece:

out {
>     assert(A.isSorted);
> } body {
>     static void bottomUpMerge(T)(in T[] A, in size_t iLeft, in 
> size_t iRight, in size_t iEnd, T[] B)
>     pure nothrow @safe @nogc {

mainly the 'out' and 'body' as well as the 'ins'

Thank you.