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Let me give a concrete example of how I've been personally impacted by the lack of generics. My project makes liberal use of pointers to represent "optional" fields, since they need to be distinguished from the zero-type. Alternatives would be to have a boolean associated with every field, but that clutters the API and still faces a lot of the problems with using pointrs, such as:

- Easy to forget to check that pointer != nil

- Overloaded semantics: it's unclear whether a pointer represents an optional type, or is being used to pass-by-refrence (i.e. unclear whether a value should be treated read-only)

- Need to deep copy every struct, which is easy to forget and inefficient (at least the reflect version)

There are solutions to each of these points, but they all add complexity (e.g. generating code), and most take a lot of extra effort. With generics I could have Optional<T>, With a Get() function returning 2 values: the value type, and present (i.e. the way maps work). The caller is forced to handle both returns, making it much harder to forget to check it.

A lot of arguments for generics focus on higher-level functional programming abstractions, but this is a simple and extremely common use-case, and the lack of a solution is responsible for many real-world bugs.




    type Optional struct {
        stuff interface{}
        present bool
    }
    
    func (o Optional) Get() (interface{}, bool) {
        return o.stuff, o.present
    }

    func NewOptional(stuff interface{}) {
        return Optional(stuff, true)
    }




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