Do EEx templates compile to iolists or binaries?

I think it depends on the specific engine you use. I think the SmartEngine concats a big binary blob (should be an iolist in my opinion, but someone else could always make a new engine to do so). EEx itself is just the parser stuff.

Oh, I see. I meant the default one. I wonder if the benchmarked apps use any other engine that emits iolists? That’d be a considerable improvement in IO throughput, I think.

Is there any engine that compiles templates to iolists?

Honestly I’ve not actually looked… ^.^;

iex(2)> EEx.eval_string "foo <%= bar %>", [bar: "baz"], [engine: IOListEngine]
[[[] | "foo "] | "baz"]

Yeah, it doesn’t seem too hard to write one. That’s a naive implementation where I just replaced empty strings with empty lists and string concatenation with list building.

SmartEngine concats a big binary blob

Yes, that’s what it does. elixir/lib/eex/lib/eex/engine.ex at v1.5.2 · elixir-lang/elixir · GitHub

But phoenix uses Phoenix.HTML.Engine which does use iolists. phoenix_html/lib/phoenix_html/engine.ex at main · phoenixframework/phoenix_html · GitHub

Ah good to know, I ‘thought’ it did but was not certain.

But they are still slower …

# render small list

iex(1)> :timer.tc(fn -> Enum.each(1..100_000, fn _ -> EExTest.custom_fortune_html([a: "a", b: "b"]) end) end)
{288843, :ok}
iex(2)> :timer.tc(fn -> Enum.each(1..100_000, fn _ -> EExTest.fortune_html([a: "a", b: "b"]) end) end)
{480979, :ok}
iex(3)> :timer.tc(fn -> Enum.each(1..100_000, fn _ -> EExTest.phoenix_fortune_html([a: "a", b: "b"]) end) end)
{384202, :ok}

# render empty list

iex(4)> :timer.tc(fn -> Enum.each(1..100_000, fn _ -> EExTest.fortune_html([]) end) end)
{142473, :ok}
iex(5)> :timer.tc(fn -> Enum.each(1..100_000, fn _ -> EExTest.phoenix_fortune_html([]) end) end)
{120085, :ok}
iex(6)> :timer.tc(fn -> Enum.each(1..100_000, fn _ -> EExTest.custom_fortune_html([]) end) end)
{74349, :ok}

# render bigger list

iex(7)> data = Enum.map(1..1000, fn i -> {i, i} end)

iex(8)> :timer.tc(fn -> Enum.each(1..1_000, fn _ -> EExTest.custom_fortune_html(data) end) end)
{293852, :ok}
iex(9)> :timer.tc(fn -> Enum.each(1..1_000, fn _ -> EExTest.fortune_html(data) end) end)
{1111719, :ok}
iex(10)> :timer.tc(fn -> Enum.each(1..1_000, fn _ -> EExTest.phoenix_fortune_html(data) end) end)
{385075, :ok}

Are you doing everything it does? They do things like auto-escaping of text so no html injections and such, lookups for values in different places, etc… etc…

That happens at compile time, doesn’t it?

Reading through phoenix_html again, I see that some of the checks are done at runtime though, yeah.

How would it? Say some user input is in a variable that is put into the template, it needs to escape that, thus a runtime call, it has all kinds of checks all over (because, for example, it shouldn’t escape that user variable if it is wrapped in a :raw 2-tuple).