3 ms·

When you want to abstract on structs "having" a given field (by name) of a given type, I think. Although that may come in Go at some point.

• tines 1y ago
  I'm not a Go expert but that's exactly what interfaces are, aren't they? In Go a struct automatically implements an interface if it contains all the required fields (duck-typing).
  • deleted 1y ago
    [deleted]
  • sparkie 1y ago
    They're both a form of structural typing - the static equivalent of duck typing. A difference with row types is that they don't have to be declared up front like an interface - they're basically anonymous types. You declare the row types in the type signature. For example, a function taking some structural subtype of `Foo` and returning some structural subtype of `Bar` would be written in Go as: type Foo interface { baz Baz } type Bar interface { qux Qux } func (x Foo) f() Bar { ... } In OCaml, you'd just inline the row types - there are no `Foo` or `Bar`: val f : < baz : Baz.t; .. > -> < qux : Qux.t; .. > let f x = ... You can typedef row types though type foo = < baz : Baz.t; .. > type bar = < qux : Qux.t; .. > val f : foo -> bar Rows can be declared to have an exact set of members. For example, the types `< bar : Baz.t >` and `< bar : Baz.t; ..>` are two different types. The latter can have members besides `bar`, but the former can only have the member `bar`. A type containing the fields `bar` and `qux` would be a subtype of `< bar : Bar.t; .. >`, but it would not be a subtype of `< bar : Bar.t >`. OCaml has another form of structural typing in its module system, closer to interfaces where a `module type` is declared up-front, and can be specified as the argument for a functor (parameterized module) - but this is incompatible with the row types in the object system.
    • logicchains 1y ago
      Go also supports inline/unnamed interfaces.
  • aatd86 1y ago
    It's not fields but methods.