Enforcing type safety for custom Hash function

[ElegantBeef]

Did you put the hash after or before the procedures that indexed the table? The 
following code works as intended but as soon as you move the value below the 
`set` and `get` it fails of course. 
    
    
    import std/[tables, hashes]
    
    proc hash(a: int): Hash =
      result = hashes.hash(a)
      echo "Used our hash"
    
    var a: Table[int, int]
    
    proc getIndex*(k: int): int =
        if a.hasKey(k):
             return a[k]
        else:
             return -1
    
    proc setIndex*(k: int, v: int) =
        a[k] = v
    
    a[100] = 300
    assert getIndex(300) == -1
    assert getIndex(100) == 300
    setIndex(3, 400)
    assert getIndex(3) == 400
    
    
    Run