What is the difference between == and =:= in Erlan

Question

Apart from the fact that =:= prevents unwanted integer casts:

1> 1=:=1.0.
false

What is the advantage of using =:= with terms in general?

Better performance?

Answer 1

The biggest advantage of =:= is it returns true only for same terms in the same way as pattern matching. So you can be sure they are same. 1 and 1 are same terms and 1 with 1.0 are not. That's it. If you write function like foo(A, B) when A =:= B -> A. and bar(A, B) when A =:= B -> B. they will behave same. If you use == it will not be same functions. It simply prevents surprise. For example, if you make some key/value storage it would not be right if you store value with key 1 and then get this value if ask for key 1.0. And yes, there is a little bit performance penalty with == but least astonishment is far more important. Just use =:= and =/= when it is your intent to compare same terms. Use == and /= only if it is your intent to compare numbers.

Answer 2

Eshell V5.9.3.1 (abort with ^G)
1> 1.0==1.
true
2> 1.0=:=1.
false
3>

see it？ when go with"==" it will tranfer the two element into the same format to match. when "=:=" do not ,when the two element is same-type and same-value will be returning true.