Attribute for forcing copies of mutable types

[kwasimensah]

I'm proposing an attribute that helps with tracking shallow copies vs deep copies/ownership semantics. I just spent a while tracking down a bug caused by this.

C++ surfaces errors like this because you're likely to pass in references as parameters but have to use values as member variables, to you're more likely to cause a copy than dangling reference

class Foo {
private /*magic_attribute */_bars : readonly string[]
constructor(bars : readonly string[]){
this._bars = bars // This line now complains because I didn't call bars.slice(0)
}
}

magic_attribute named something like owning_copy? copy_mutables?
I'm working with TypesScript 3.6.4

[nmain]

See #16148

[RyanCavanaugh]

Please use the issue template next time. Thanks!

[kwasimensah]

Ah, sorry for not seeing the template (thought it was just boilerplate about trying to find dupes).

Looking at the context bug, ownership seems well litigated. How about something that tracks frozenness? That would get the immutability check I’m really trying to get at

[kwasimensah]

In case anyone else runs into this, the ReadOnly type wrappers does exactly this, carry the frozen of an an object through the type system.