Why do "const inout" and "const inout shared" exist?

[Walter Bright via Digitalmars-d]

On 7/2/2017 1:12 AM, Sönke Ludwig wrote:
> The idea is to be able to write: string result = foo(true, "bar");

If it is declared as:

     inout(char)[] foo(bool condition, inout(char)[] chars);

your specific case will work as expected. Perhaps you meant:

    char[] s;
    string result = foo(true, s);

which will never work, even if const inout is a type, because the returns in the 
function body do NOT determine the return type's inout meaning. Only the type of 
the argument supplied to the inout parameter does that.


> However, in this case it can be also argued that supporting this specific case 
> adds it's own complexity. The concept of const(inout(T)) definitely sounds like 
> one of the harder ones to explain. So I'd probably still opt for simplifying the 
> conversion hierarchy.

Neither I nor anyone here seems to understand its purpose. The existence of it 
is likely a significant contributor to peoples' confusion about inout.

It's my fault as I should have noticed this getting slipped into the compiler.