Const: what do you want to achieve (proposition...)?

[David B. Held]

Gilles G. wrote:
> You misunderstood the proposition: it implies that all parameters given to a function would be const *except* if they are returned by the function.
> So, in the example you give, if you wanted to be sure that val is not modified, you would just call:
> myFunctionReturningVoid(val);
> 
> A function which wants to change its arguments would *have to* pass them as return values.
> 
> For example this function:
> Foo myFunction(Foo foo){
>     foo.value = 0;
>     return foo;
> }
> could be called like this:
> myFunction(myFoo);   // don't modify myFoo since parameters are const by default
> myFoo2 = myFunction(myFoo); // still don't modify myFoo
> myFoo = myFunction(myFoo);   // this is the *only* way to modify myFoo: it is explicit
> It would be up to the compiler to decide if the parameters must be passed by value, reference, (or whatever) to acheive constness.
> [...]

 From a pure functional point of view, that's all well and good.  But D 
allows in-place mutation, and that means functions have to be allowed to 
have out parameters that look like out parameters.

Dave