slices | Go slice helper functions | Functional Programming library

Update: Since GitHub pull request #93755 has been merged, comparison between Vecs with different allocators is now possible.

Original answer:

Vec uses the std::alloc::Global allocator by default, so Vec is in fact Vec. Since Vec and Vec are indeed distinct types, they cannot directly be compared because the PartialEq implementation is not generic for the allocator type. As @PitaJ commented, you can compare the slices instead using assert_eq!(&a[..], &b[..]) (which is also what the author of the allocator API recommends).

From the Go 1.18 release notes:

The Go compiler does not support accessing a struct field x.f where x is of type parameter type even if all types in the type parameter's type set have a field f. We may remove this restriction in Go 1.19.

You could for example add a DateStart() time.Time method to each of the structs that returns the DATE_START field, and then use that method as part of your type constraint if you wanted to use generics.

That said, you don't need generics for this specific problem. Even without generics, you could define an interface:

The issue you're hitting is that -0 is the same as 0, and x[0:0] is an empty slice.

I'd suggest:

I've passed your code through gotip that uses a more evolved implementation of the proposal and it does not complain about that part of the code, so I would assume that the problem is with the go2go initial implementation.

Please note that your implementation will not work since you can definitely use parametric interfaces in type assertion expressions, but you can't use interfaces with type lists as you are doing in testDifference[intOrString]

It matters if you have to return a slice of the same (possibly named) type as the argument.

If you do not have to return a slice (just some other info e.g. a bool to report if the value is contained), you do not need to use a type parameter that itself constraints to a slice, you may use a type parameter for the element only.

If you have to return a slice of the same type as the input, you must use a type parameter that itself constraints to a slice (e.g. ~[]E).

To demonstrate, let's see these 2 implementations of Grow():

No, you can't.

By definition of the orphan rules:

Given impl Trait for T0, an impl is valid only if at least one of the following is true:

• Trait is a local trait
• All of
  • At least one of the types T0..=Tn must be a local type. Let Ti be the first such type.
  • No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti)

Only the appearance of uncovered type parameters is restricted. Note that for the purposes of coherence, fundamental types are special. The T in Box is not considered covered, and Box is considered local.

Local trait

A trait which was defined in the current crate. A trait definition is local or not independent of applied type arguments. Given trait Foo, Foo is always local, regardless of the types substituted for T and U.

Local type

A struct, enum, or union which was defined in the current crate. This is not affected by applied type arguments. struct Foo is considered local, but Vec is not. LocalType is local. Type aliases do not affect locality.

As neither Index nor Range nor Vec are local, and Range is not a fundamental type, you cannot impl Index<...>> for Vec, no matter what you put in the place of the ....

The reason for these rules is that nothing prevents Range or Vec from implementing impl Index> for Vec. Such impl does not exist, and probably never will, but the rules are the same among all types, and in the general case this definitely can happen.

You cannot overload the range operator either - it always creates a Range (or RangeInclusive, RangeFull, etc.).

The only solution I can think about is to create a newtype wrapper for Vec, as suggested in the comments.

If you want your vector to return a wrapped slice, you can use a bit of unsafe code:

Since your children's children has same structure as children, you can try using json_normalize twice separately and append it together.

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