Add eenv_appname:get_/1/2 [ENHANCEMENT]

[yhafri]

Would it be possible to also generate get_/1,get_/2 functions like these:

% eenv_appname.beam
-module(eenv_appname).

-export([get/1]).
-export([get_/1, get_/2]).

get(ip) -> {ok, "127.0.0.1"};
get(_)  -> undefined.

%% extra API
get_(ip) -> "127.0.0.1";
get_(_)  -> undefined.

get_(Key, Default) ->
  case get_(Key) of
     undefined -> Default;
     Value -> Value
  end.

The idea with get_/1 is to return the value immediately, and avoid matching against the tuple {ok, Value} in the caller.

Second, get_/2 will return a default value instead of getting undefined.

As you may have noticed, I've added an underscore _ suffix to these new calls to not clash with the original get/1.

[yhafri]

New eenv_router.erl module for consistency.

% eenv_router.beam
-module(eenv_router).

-export([get/2]).
-export([get_/2, get_/3]).

get(appname_1, Key) -> eenv_appname_1:get(Key);
get(appname_2, Key) -> eenv_appname_2:get(Key);
get(_, _) -> unload.

%% extra API
get_(appname_1, Key) -> eenv_appname_1:get_(Key);
get_(appname_2, Key) -> eenv_appname_2:get_(Key);
get_(_, _) -> unload.

get_(appname_1, Key, Default) -> eenv_appname_1:get_(Key, Default);
get_(appname_2, Key, Default) -> eenv_appname_2:get_(Key, Default);
get_(_, _,_) -> unload.

[yhafri]

A better idea IMHO. The whole purpose of erl-env is to speed up application:get_env, right?
So why not go one level down, and produce this instead:

% eenv_appname.beam
-module(eenv_appname).

-export([get/1]).

-export([ip/0, port/0]).
-export([get_/1,get_/2]).

get(ip) -> {ok, "127.0.0.1"};
get(port) -> {ok, 8080};
get(_)  -> undefined.

%% extra API

ip() -> "127.0.0.1".
port() -> 8080.

get_(ip) -> "127.0.0.1";
get_(port) -> 8080;
get_(_) -> undefined.

get_(ip, _) -> "127.0.0.1";
get_(port, _) -> 8080;
get_(_, Default) -> Default.

[zhongwencool]

In my option:

1. It would not increase speed with cutting down the {ok, Value} to Value(The difference is too small to be measured). But this will cause one confusion when it return undefined, this mean the key is missing or value is 'undefined' ?

ip() -> "127.0.0.1".
port() -> 8080.

This assuming that the Module find function is more efficient than function clause match?
I only know the function clause match is binary tree search. It's fast.
I don't know how module find function. maybe you can prove this by benchmark.

Inconvenient: Caller will make sure the key is exist. I think this will too low level down for normal user.

3. Make the Default into function clause.

The original method just have one atom argument. It make the search as simple as possible.
And It would not hit the default branch and only hit the match clause at most of time in production environment.

The new method increase one argument, and no use most of time， Not sure the compile can optimize
this function clause.

Change to new method is very simple, you can do it and add a small benchmark in eenv_benchmark.erl to see.

PR is welcome~