Erlang Thursday – erlang:list_to_atom/1

Today’s Erlang Thursday covers erlang:list_to_atom/1.

erlang:list_to_atom/1 takes a string, and returns an Erlang atom.

list_to_atom("foo").
% foo
list_to_atom("Foo").
% 'Foo'
list_to_atom("Foo_bar").
% 'Foo_bar'
list_to_atom("foo_bar").
% foo_bar
list_to_atom("foo"++"bar").
% foobar
list_to_atom("Erlang").
% 'Erlang'
list_to_atom("Elixir").
% 'Elixir'

This can be useful if you are having to create keys or identifiers based off strings read in from outside the system, such as parsing a CSV style header.

lists:map(fun erlang:list_to_atom/1,
          string:tokens("firstName,lastName,age,gender,preferredName,dateOfBirth", ",")).
% [firstName,lastName,age,gender,preferredName,dateOfBirth]

You do need to be careful when using erlang:list_to_atom/1 on strings acquired from the outside world of your program, as it only handles strings with character values under 256. But any character value1 under 256 is fair game to be turned into an atom.

list_to_atom("Joe, Mike, and Robert").
% 'Joe, Mike, and Robert'
list_to_atom("it's").
% 'it's'
list_to_atom("heyn").
% 'heyn'€
list_to_atom("with_supported_char"++[255]).
% with_supported_charÿ
list_to_atom("with_non_supported_char"++[256]).
% ** exception error: bad argument
%      in function  list_to_atom/1
%         called as list_to_atom([119,105,116,104,95,110,111,110,95,115,117,112,112,111,114,
%                                 116,101,100,95,99,104,97,114,256])

–Proctor


1. Remember that character values are non-negative integer values as well. 0-255 inclusive. back

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