为什么未定义此erlang函数？

Question

iex(1)> a = :erlang.timestamp
{1458, 585479, 931609}
iex(2)> b = :erlang.timestamp
{1458, 585484, 197713}
iex(3)> :erlang.now_diff(a,b)
** (UndefinedFunctionError) undefined function: :erlang.now_diff/2
    :erlang.now_diff({1458, 585479, 931609}, {1458, 585484, 197713})

So I can access erlang functions in elixir, accessing them by :erlang , but now_diff/2 is undefined.

I have a thought that this timer is not standard erlang module, and needed to be required/imported, but I can't figure out how?

PS Don't advice timex instead if it doesn't have function to calculate timestamps diff with high precision like this erlang function. I didn't find reading docs.

Answer 1

Use

:timer.now_diff(a, b)

Functions are not prefixed with :erlang because they are erlang functions, but because they are part of the erlang module. now_diff is part of the timer module, hence you would use :timer instead of :erlang .