Propagating constness through function results

[Steven Schveighoffer]

On 9/17/17 5:37 PM, David Zhang wrote:
> Nevermind! I rediscovered the `inout`attribute.

Correct, inout applied to the function is actually applying to the 
'this' parameter. Same as const or immutable functions as well.

> 
> Though if I may say so, I have no idea how `inout` is supposed to 
> indicate "whatever the constness of a".
> 

What inout does is look at the mutability of the parameter and transfer 
it to the mutability of the return type.

-Steve