Structs’ success typing is the same as common garden maps to Dialyzer, right? What are the preferred ways to enforce a particular struct?

Erlang 19 introduces more advanced support from dialyzer for maps - checking specific keys and general key types. Support for those new features is in Elixir 1.3 as well. Here’s the PR that introduced them: https://github.com/elixir-lang/elixir/pull/4662

In Elixir you can pattern match on the struct’s type so for example: defmodule StructTest do defstruct name: "Foo!" end defmodule TestStruct do def takesStruct(struct = %StructTest{}) do IO.puts(inspect struct) end end The takesStruct function will only match for instances of …

You can see more information at the Typespecs page in the Documentation . To match a Struct inside a typespec, use the normal %StructName{} syntax. EDIT: The documentation moved to a new location.

As far as I can see Dialyzer likens structs to any general map %{}, which means you lose the specificity…

1.3 rc0 was just released today.

Erlang 19-rc was released couple days ago. I’d expect final release probably in the matter of next couple weeks.

Hello! I am totally new to Elixir and I just found your response because I am trying to figure out this pattern matching for types is def takesStruct(struct = %StructTest{}) do equivalent to def takesStruct(%StructTest{} = struct) do? As I understand, def takesStruct(%StructTest{} = struct) do i…

It’s just matching on a %StructTest, empty or not, you can’t have a struct that is empty, since a struct is just a map with pre-defined fields. You can match on an empty map though, with a guard clause, def empty(%{} = variable) when variable == %{} do , or on empty struct fields directly def empty(…

[image] miguelsaddress: As I understand, def takesStruct(%StructTest{} = struct) do is checking that struct is of type StructTest, am I right? or is it explicitly requiring an empty struct? (I dont think it is even possible…) def takesStruct(%StructTest{} = struct) do, means: this function…

Thank you both, now it is clear :slight_smile:

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Type Checking Structs

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mmport80 May 30, 2016, 2:01pm 6

oh really? this is very nice. when’s the eta? (if there is one)