Hi All,
New to Nim (background is Go, Python, Java/C#, very rusty C) and struggling to
understand the use for `ptr object` types.
The docs say
> As a syntactical extension, object types can be anonymous if declared in a
> type section via the `ref object` or `ptr object` notations
This seems to work as I would expect using the constructor syntax for `ref
object` types (the result is basically what you would consider a "normal" type
in Java or a `*` type in Go, right?) - so I can mutate it in procs/methods
without copying it.
type Person = ref object
name: string
var person = Person(name: "James")
echo person.name
Run
But I am struggling to construct a `ref object` object. I either cannot
construct it with a compiler error, or I get a SIGSEGV on the `create()d`
memory at runtime. I can construct and take a pointer to a "normal" object just
fine. So what is the use case for `ptr object`. This doesn't seem to be
discussed in the docs at all.
type Cat = object
name: string
type DangerousCat = ptr object
name: string
enjoysMemoryLeaks: bool
# All good, can make pointer to normal object type
var cat = Cat.create()
cat[] = Cat(name: "Top Cat")
echo cat.name
dealloc(cat)
# Compile Error: object constructor needs an object type
var dangerCat = DangerousCat.create()
dangerCat[] = DangerousCat(name: "Garfield")
echo dangerCat.name
dealloc(dangerCat)
# SIGSEGV: Illegal storage access
var dangerCatSigSegV = DangerousCat.create()
dangerCatSigSegV.name = "Garfield"
echo dangerCatSigSegV.name
dealloc(dangerCatSigSegV)
Run
PS. This is purely for curiousity, I know that the `ptr` stuff has very limited
application in real life and I should be using `ref` for my objects (I guess
like in Go, using `*Struct` instead of `Struct` 99% of the time unless it is a
small struct staying locally in the current function...)
Thanks!
