Target Type Propagation

[DavePearce]

Consider the following Whiley function:

function f(int[] xs) -> (int[] rs):
   xs[0] = 0
   return xs

This currently compiles to the following Java:

public static BigInteger[] f(BigInteger[] xs) {
    xs[BigInteger.valueOf(0L).intValue()] = BigInteger.valueOf(0L);
    return xs;
}

The basic issue is that from the array access we want to propagate forwards the fact that it is expecting a Java int. This could then be used when translating the constant to produce this:

   xs[0] = ...

There are presumably other situations when this might be useful ...