Stepping back and looking at constness from another angle.

[David B. Held]

Regan Heath wrote:
> [...]
> - local variables are (until manually/explicitly assigned to another such)
> the 1st and only copy/reference of/to the data.
> 
> - function parameters are implicitly a copy/alias of data.  Once you have
> aliases you have complication and once you have complication you greatly
> increase the chances of unexpected changes and therefore bugs.
> [...]

Ok, Bruno probably won't like this, but he makes a great point about 
orthogonality.  The killer argument for orthogonality, IMO, is generics. 
  Remember that function argument lists are type tuples.  If we say that 
function arguments are const by default, that means that a given type 
tuple has different meanings depending on whether it is used in a 
function argument context or a non-function argument context.  In fact, 
it could have exactly the *opposite* meaning, which would be the worst 
kind of non-orthogonality.  This may seem like a faraway problem, 
because I don't believe you can construct functions by assembling type 
tuples and pasting them onto bits of code.  But if we cement in this bit 
of non-orthogonality, we guarantee that such a feature is either awkward 
or impossible in the future.

Dave