erlang - Is there a way to do lookups on default record values? -

given record

-record(something, {id                :: integer(),                     name              :: string(),                     email = undefined :: string() | undefined}). 

is there way default values fields, in example getting fact #something.email defaults undefined?

records syntactic sugar in erlang, expanded compiler. following solution, suggested @dmitry, works, compiler not optimize away unless pass +inline, since trick here create record:

g() -> (#something{})#something.email. 

such record syntactic sugar expanded to: (use erlc -e)

g() ->     case {something,undefined,undefined,undefined} of         {something,_,_,rec0} ->             rec0;         _ ->             error({badrecord,something})     end. 

and become: (use erlc -s)

{function, g, 0, 4}.   {label,3}.     {line,[{location,"test.erl",10}]}.     {func_info,{atom,test},{atom,g},0}.   {label,4}.     {move,{literal,{something,undefined,undefined,undefined}},{x,0}}.     {test,is_tuple,{f,5},[{x,0}]}.     {test,test_arity,{f,5},[{x,0},4]}.     {get_tuple_element,{x,0},0,{x,1}}.     {get_tuple_element,{x,0},3,{x,2}}.     {test,is_eq_exact,{f,5},[{x,1},{atom,something}]}.     {move,{x,2},{x,0}}.     return.   {label,5}.     if_end. 

the #something.email part of expression not means getting email field of created record, checking passed record formed. test not optimized default. fortunately, can optimize -compile([inline]). in module or +inline on command line.

the following solution simpler compiler:

f() -> element(#something.email, #something{}). 

record syntactic sugar (here #something.email index of email field) expand to:

f() ->     element(4, {something,undefined,undefined,undefined}). 

in case, not tell erlang test #something{} being proper #something record. compiler optimizes calls element/2 built-in function. become:

{function, f, 0, 2}.   {label,1}.     {line,[{location,"test.erl",7}]}.     {func_info,{atom,test},{atom,f},0}.   {label,2}.     {move,{atom,undefined},{x,0}}.     return. 

please note default value field is undefined unless explicitly provided. result, code:

-record(something, {id                :: integer(),                     name              :: string(),                     email = undefined :: string() | undefined}). 

is equivalent to:

-record(something, {id    = undefined :: integer() | undefined,                     name  = undefined :: string()  | undefined,                     email = undefined :: string()  | undefined}). 

yet, code seems mean id integer() , never undefined, , likewise name string(). untrue. if mean, should provide default value different undefined:

-record(something, {id    = 0   :: integer(),                     name  = ""  :: string(),                     email       :: string()}). 

only providing default value tell dialyzer id , name can never undefined.