CODEWITHSUNDEEP
typeserlangtypecheckingcustom-type
Stratus3D
Stratus3D

Reputation: 4906

Check if variable is of a custom type in Erlang?

Is there a way to check if a variable is of a custom type in Erlang?

Suppose I have some records and types defined in an .hrl file:

-record(custom_record, {
    attr1 :: list(),
    attr2 :: binary(),
    attr3 :: tuple()
}).

-record(another_record, {
    attr1 :: list(),
    attr2 :: binary(),
}).

-type custom_record() :: #custom_record{}.

-type another_record() :: #another_record{}.

-type custom_records() :: custom_record() | another_record().

Is there an easy way to check if a record is a custom_record in my Erlang code? Something like this would be nice:

is_custom_type(CustomRecord, custom_records). %=> true

I looked through the docs and didn't see any build-in functions that did this.

Upvotes: 2

Views: 3699

Answers (3)

Odobenus Rosmarus
Odobenus Rosmarus

Reputation: 5998

The Erlang standard library contains the is_record() BIF, that checks if the first element of a tuple is the appropriate atom, see is_record/2 so you can test your variable like is_record(Var, custom_record).

Upvotes: 7

Dmitry Belyaev
Dmitry Belyaev

Reputation: 2593

There are no custom types in Erlang. Records are just syntactic sugar for tuples tagged with the atom and of the same length. Typespecs are used solely by dialyzer and nothing else.

Upvotes: 2

mkorszun
mkorszun

Reputation: 4571

You could use pattern matching for this purpose:

is_custom_type(#custom_record{} = _Record) -> true;
is_custom_type(_) -> false.

Upvotes: 1

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