ACLs for variables - lock / unlock idea

[Cecil Ward]

On Friday, 29 September 2017 at 13:07:32 UTC, Atila Neves wrote:
> auto modifiable = foo();
> {
>     const nonModifiable = modifiable;
>     //...
> }

I had already thought about using two names.

I don’t think that using a kind of ‘const-alias’ mechanism (or 
‘const reference’, in the C++ var& sense) would be a good idea at 
all. By this I mean something where a modifiable variable has two 
names, only of of them permitting write access. The reason why 
this wouldn’t be good enough is that there would be nothing much 
stopping me from forgetting what I’m doing and going back to 
using the wrong name at some point, without any warnings. Slight 
mitigation would be if the original declaration was something 
like myvar_writeable and the const alias for it was called simply 
myvar, so that the default brain-free form would be the safe one 
and you would have to go out of your way to get write access. It 
still wouldn’t be that strong though.

Iirc you get told off if you block access to variables by using 
‘shadowing’, declaring an exactly matching name using an alias 
declaration in a normal basic block scope. (I suspect you can do 
so inside function bodies, I don’t think d moans about you 
blocking access to matching variables that are in global or 
outer, non-global, non-local scopes if you write ‘shadowing’ 
local variable declarations - not sure.) Anyway, couldn’t use 
that either and it’s no way usable enough for me.