Structs in Erlang

Go’s structs are typed collections of fields. They’re useful for grouping data together to form records.

This person struct type has name and age fields.

-module(structs).
-export([new_person/1, main/0]).

-record(person, {name, age = 0}).

new_person(Name) ->
    #person{name=Name, age=42}.

main() ->

    % This syntax creates a new struct
    io:format("~p~n", [#person{name="Bob", age=20}]),

    % You can name the fields when initializing a struct
    io:format("~p~n", [#person{name="Alice", age=30}]),

    % Omitted fields will be zero-valued
    io:format("~p~n", [#person{name="Fred"}]),

    % An & prefix yields a pointer to the struct
    P1 = #person{name="Ann", age=40},
    Ptr1 = erlang:make_ref(),
    io:format("~p~n", [Ptr1]),

    % It’s idiomatic to encapsulate new struct creation in constructor functions
    io:format("~p~n", [new_person("Jon")]),

    % Access struct fields with a dot
    S = #person{name="Sean", age=50},
    io:format("~p~n", [S#person.name]),

    % You can also use dots with struct pointers - the pointers are automatically dereferenced
    SP = &S,
    io:format("~p~n", [SP#person.age]),

    % Structs are mutable
    NewSP = setelement(2, SP, 51),
    io:format("~p~n", [NewSP#person.age]),

    % If a struct type is only used for a single value, we don’t
    % have to give it a name. The value can have an anonymous
    % struct type.
    Dog = #{name => "Rex", isGood => true},
    io:format("~p~n", [Dog]).

To run the program, compile it and then execute the main function.

$ erlc structs.erl
$ erl -noshell -s structs main -s init stop
#person{name = "Bob", age = 20}
#person{name = "Alice", age = 30}
#person{name = "Fred", age = 0}
#Ref<0.0.0.106>
#person{name = "Jon", age = 42}
"Sean"
50
51
#{isGood => true, name => "Rex"}

Now that we can run and build basic Erlang programs, let’s learn more about the language.

Strings and Runes in Erlang

Methods in Erlang

Learn X By Example

Title here

Structs in Erlang