Overloading assignment

ID:2534755
 
Jan 3 2020, 6:51 pm
Resolved
A new "assign-into" operator := has been added, which can be overloaded. This allows more flexibility in advanced datum types.
Applies to:DM Language
Status: Resolved (514.1543)
This issue has been resolved.
Obviously we can't overload the standard = assignment operator because it would be a horrendous mess and probably the assumption of assignment actually changing the value stored in a variable instead of modifying an object stored in that variable is a deeply-embedded assumption in the code. As an alternative, could we get some sort of additional operation that takes on this role, something like := or <- or something like that? Then we could do something like
var/Unsigned32/int = new

// Stores the value '123456' (whatever "stores" should be
// taken to mean for the object in question) instead of
// the int variable having that value.
int <- 123456
// or
int := 123456

world << ((int == 123456) ? "True" : "False") // "False"
world << ((int ~= 123456) ? "True" : "False") // "True"
Jan 5 2020, 11:42 pm
I get the use case you're going for: you want something like where a datum can take an assignment and update its internal values, much like you can assign a char const* to a user-defined string type in C++ and it'll make the necessary arrangements under the hood.

I suppose adding an operator for this purpose might be possible, but it's basically no more than syntactic sugar for a proc call. It'd end up being equivalent to object.AssignSomething() since it'd just be looking up the appropriate operator proc and executing that.
Jan 10 2020, 12:19 am
Yeah, I'm aware. I'm more interested in making the object behaving as a "pseudo-variable" more transparent, even though it is very much just syntactic sugar.
Jan 10 2020, 12:35 am (Edited on Jan 10 2020, 12:40 am)
What about a property-like syntactic sugar? (Slightly different purpose, I'm aware, but similar in use I think.)

// Better syntax TBD.

/mytype/var/__age

/mytype/proc/__get_age()
    return __age

/mytype/proc/__set_age(age)
    if (!isnum(age) || age < 0 )
        throw // ...
    __age = age

// Usage.

var/mytype/m = new
m.age = -1 // Throws.
Jan 10 2020, 12:43 am
In response to Hiead
Hiead wrote:
What about a property-like syntactic sugar? (Slightly different purpose, I'm aware, but similar in use I think.)

> // Better syntax TBD.
>
> /mytype/var/__age
>
> /mytype/proc/__get_age()
>     return __age
>
> /mytype/proc/__set_age(age)
>     if (!isnum(age) || age < 0 )
>         throw // ...
>     __age = age
>
> // Usage.
>
> var/mytype/m = new
> m.age = -1 // Throws.
>

That would be insanely useful.
Jan 10 2020, 12:48 am
In response to Hiead
Properties have been something I've wanted for years. They're incredibly helpful.
Jan 10 2020, 1:07 pm
I design systems where reassignment of variables directly have consequences. This means I need to train anyone who uses my code how the library or snippet works at a deep level, and field lots of questions as to why my code breaks when you use it in a way the documentation explicitly tells you not to.

This would make Ter a happy bear, able to hibernate in his cave with less disturbances.
Jun 9 2020, 2:13 pm
This is implemented for BYOND 514. The issue will be closed when the first beta is released.
Jun 9 2020, 2:14 pm
In response to Lummox JR
What exactly is implemented here?
Jun 10 2020, 7:35 pm
In response to Kaiochao
There's a new overloadable := operator, which has overload procs defined for some of the built-in datums but for others you'll have to define it yourself. This is called the "assign into" operator.
Feb 1 2021, 8:47 am
Lummox JR resolved issue with message:
A new "assign-into" operator := has been added, which can be overloaded. This allows more flexibility in advanced datum types.