[erlang-questions] newbie: why c.erl is special?

[Daniel Luna]

On Wed, 5 Mar 2008, Bengt Kleberg wrote:
> Greetings,
>
> How does the erlang run time handle 2 modules called lists?
>
> Which lists module will those other modules that have not done
> -import_as(lists, stdlib_lists).
> get?

Even more interesting: What will happen if you have two (or three...) 
modules all doing the below magic?

What module will you really call when you do lists:reverse/1?

(Or even worse; what module will you call when you do Mod:reverse(List) 
inside one of these modules? (Mod was an argument coming from outside the 
module))

Etc...

/Luna

> bengt
>
> On Wed, 2008-03-05 at 21:23 +1100, Anthony Kong wrote:
>> Hi, Shiwei,
>>
>> I'd concur that a capability to alias an imported module sounds like
>> an attractive idea.
>>
>> I personally would prefer a new directive called "import_as".
>>
>> ======
>> -module(lists). %% I want to call my module lists too.
>> -import_as(lists, stdlib_lists).
>>
>> ...
>> lists:copycat() ->
>>   stdlib_lists:reverse([a,b,c]). %% essentially calling lists:reverse([a,b,c])
>>
>> ======
>>
>> Just the same as your idea of "-alias".
>>
>> Until then, I probably have to learn to live in this namespace flatland :-)
>>
>> Cheers, Anthony
>>
>>
>>
>> 2008/3/1 shiwei xu <xushiweizh@REDACTED>:
>>> I think flat module namespaces is a defect of erlang design.
>>>
>>> For example, I write a foo.erl, It works well. But maybe in a late erlang
>>> version (eg. R13B)  also write such  module named  foo.erl. Then,  you can
>>> see  my application goes wrong.
>>>
>>> How to avoid things like this? Let's see the following ways:
>>>
>>> 1. Adjust module searching paths, and let user path (which contains my
>>> foo.erl) take precedence over erlang stdlib/otp path. But, this way can't
>>> always work well. If some other stdlib/otp modules use system foo.erl (not
>>> my foo.erl), Things goes wrong.
>>>
>>> 2. Write erlang modules always named with a prefix (a fake namespace. For
>>> example, projectname_foo.erl or organization_projectname_foo
>>> .erl). This way really can solve the problem. But, It seems ugly.
>>>
>>> Is there a way let's user still can call foo:func (not call foo.erl provied
>>> by stdlib/otp, but my projectname_foo.erl)? I have a suggestion:
>>>
>>> Can erlang provide a 'module name alias'? That is, I can rename a module's
>>> name temporarily in a module? For example:
>>>
>>> -module(a_module_that_call_my_foo).
>>> -alias(foo, organization_projectname_foo). %% alias
>>>
>>> some_func_call_foo() ->
>>>     foo:func().  %% same as: organization_projectname_foo:func()
>>>
>>> Currently I can do this by using the 'define' keyword. For example:
>>>
>>> -module(a_module_that_call_my_foo).
>>>  -define(FOO, organization_projectname_foo). %% alias
>>>
>>> some_func_call_foo() ->
>>>     ?FOO:func().
>>>
>>> It works well, but a bit ugly.
>>>
>>>
>>>
>>> On Sat, Mar 1, 2008 at 6:51 AM, Matt Stancliff <sysop@REDACTED> wrote:
>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Feb 29, 2008, at 14:34, Anthony Kong wrote:
>>>>
>>>>> If I rename c.erl to something else, the problem goes away.
>>>>>
>>>>> What is special about "-module(c)" ?
>>>>
>>>>   Welcome to the world of flat module namespaces.
>>>>
>>>>   The code module is your friend in these circumstances.
>>>>   Look into code:clash() and code:which(module).
>>>>
>>>>   code:which(c) should return "<base path>/lib/erlang/lib/stdlib-
>>>> <ver>/ebin/c.beam"
>>>>
>>>>
>>>> -Matt
>>>> --
>>>> Matt Stancliff            sysop@REDACTED
>>>> AIM: seijimr              iPhone: 678-591-9337
>>>> "The best way to predict the future is to invent it." --Alan Kay
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> erlang-questions mailing list
>>>> erlang-questions@REDACTED
>>>> http://www.erlang.org/mailman/listinfo/erlang-questions
>>>>
>>>
>>>
>>> _______________________________________________
>>>  erlang-questions mailing list
>>>  erlang-questions@REDACTED
>>>  http://www.erlang.org/mailman/listinfo/erlang-questions
>>>
>>
>>
>>
>
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@REDACTED
> http://www.erlang.org/mailman/listinfo/erlang-questions
>

-- 
Daniel Luna                           | Top reasons that I have a beard:
luna@REDACTED                     |  a) Laziness.
http://www.update.uu.se/~luna/        |  b) I can.
Don't look at my homepage (it stinks).|  c) I can get away with it.