lua-resty-mysql design question

lionel.duboeuf · 2014-10-07T15:35:59+00:00

so you managed to compile it? 2014-10-08 17:23 GMT+02:00 Roni McGuinness <roni...@gmail.com>: > Dearest agentzh and Mex its take...

lua-resty-mysql design question

lionel.duboeuf

hello,

Just would like to know why functions are defined like this:

local function read_result(self, est_nrows)
....
end
_M.read_result = read_result

local function send_query(self, query)
....
end
_M.send_query = send_query

why not declare functions directly like this ?:

function _M.read_result(self, est_nrows)
...
end

function _M.send_query(self, query)
...
end

thanks
lionel

manchev

Most likely these functions are used internally by the module so there's no point in calling them like _M.read_result but rather by using the local function.

I guess it would have some performance overhead too if going through the module instead of using the local function.

Best,
Vladislav

On Tue, Oct 7, 2014 at 10:35 AM, Lionel Duboeuf <lionel...@gmail.com> wrote:

hello,

Just would like to know why functions are defined like this:

local function read_result(self, est_nrows) .... end _M.read_result = read_result local function send_query(self, query) .... end _M.send_query = send_query

why not declare functions directly like this ?:

function _M.read_result(self, est_nrows) ... end function _M.send_query(self, query) ... end

thanks
lionel

.

lionel.duboeuf

I see,
I understand when to use local functions but don't see why in this case we define an alias such as

_M.send_query = send_query. is it for performance purpose, isolation or only to make public a function that is mostly local ?

regards
lionel

Le mardi 7 octobre 2014 12:37:44 UTC+2, Vladislav Manchev a écrit :

Most likely these functions are used internally by the module so there's no point in calling them like _M.read_result but rather by using the local function.

I guess it would have some performance overhead too if going through the module instead of using the local function.

Best,
Vladislav

On Tue, Oct 7, 2014 at 10:35 AM, Lionel Duboeuf <lionel....@gmail.com> wrote:
hello,

Just would like to know why functions are defined like this:

local function read_result(self, est_nrows) .... end _M.read_result = read_result local function send_query(self, query) .... end _M.send_query = send_query

why not declare functions directly like this ?:

function _M.read_result(self, est_nrows) ... end function _M.send_query(self, query) ... end

thanks
lionel

.

manchev

This idiom serves both isolation and performance purposes in this case as far as I see when looking at code.

It does not allow you to directly change module's internal workings from the outside and also speeds up performance.

You can refer to the module definition page [1] in the lua-users wiki for more information and examples, it should be helpful to clear things up.

[1]: http://lua-users.org/wiki/ModuleDefinition

Best,
Vladislav

On Wed, Oct 8, 2014 at 10:48 AM, Lionel Duboeuf <lionel...@gmail.com> wrote:

I see,
I understand when to use local functions but don't see why in this case we define an alias such as _M.send_query = send_query. is it for performance purpose, isolation or only to make public a function that is mostly local ? regards lionel
Le mardi 7 octobre 2014 12:37:44 UTC+2, Vladislav Manchev a écrit :
Most likely these functions are used internally by the module so there's no point in calling them like _M.read_result but rather by using the local function.

I guess it would have some performance overhead too if going through the module instead of using the local function.

Best,
Vladislav

On Tue, Oct 7, 2014 at 10:35 AM, Lionel Duboeuf <lionel....@gmail.com> wrote:
hello,

Just would like to know why functions are defined like this:

local function read_result(self, est_nrows) .... end _M.read_result = read_result local function send_query(self, query) .... end _M.send_query = send_query

why not declare functions directly like this ?:

function _M.read_result(self, est_nrows) ... end function _M.send_query(self, query) ... end

thanks
lionel

.

luis.gasca

I would say this is for performance. Accessing locals is much faster. Take a look at Lua Programming Gems sample chapter about Lua performance tips [1]

[1] http://www.lua.org/gems/sample.pdf

El martes, 7 de octubre de 2014 09:35:58 UTC+2, Lionel Duboeuf escribió:

hello,

Just would like to know why functions are defined like this:

local function read_result(self, est_nrows) .... end _M.read_result = read_result local function send_query(self, query) .... end _M.send_query = send_query

why not declare functions directly like this ?:

function _M.read_result(self, est_nrows) ... end function _M.send_query(self, query) ... end

thanks
lionel

lionel.duboeuf

Le 08/10/2014 11:59, Vladislav Manchev a écrit :

This idiom serves both isolation and performance purposes in this caseas far as I see when looking at code.
It does not allow you to directly change module's internal workingsfrom the outside and also speeds up performance.
You can refer to the module definition page [1] in the lua-users wikifor more information and examples, it should be helpful to clearthings up.
[1]: http://lua-users.org/wiki/ModuleDefinition


ok,i see better now.
Thanks for all


regards
lionel

anorov.vorona

Not to dig up an old discussion, but...

>http://luajit.org/ext_ffi_tutorial.html

>This is less important with LuaJIT, since the JIT compiler optimizes hash-table lookups a lot and is even able to hoist most of them out of the inner loops. It can't eliminate all of them, though, and it saves some typing for often-used functions. So there's still a place for this, even with LuaJIT.

LuaJIT is generally able to optimize hash table lookups, so in reality there shouldn't be a serious performance impact from calling functions that are inside a local (not global) table. It's still considered best practice to stick with locals as much as possible though.

On Wednesday, October 8, 2014 8:21:32 AM UTC-4, Lionel Duboeuf wrote:

Le 08/10/2014 11:59, Vladislav Manchev a écrit :
> This idiom serves both isolation and performance purposes in this case
> as far as I see when looking at code.
>
> It does not allow you to directly change module's internal workings
> from the outside and also speeds up performance.
>
> You can refer to the module definition page [1] in the lua-users wiki
> for more information and examples, it should be helpful to clear
> things up.
>
>
> [1]: http://lua-users.org/wiki/ModuleDefinition
>
>

ok,i see better now.
Thanks for all

regards
lionel