[erlang-questions] Defining static functions in abstract modules
Matthew Dempsky
matthew@REDACTED
Wed Apr 9 11:22:46 CEST 2008
Because I want to be able to abstract away how to instantiate a
module, and I want to be able to define internal helper functions to
do it, and I want to be able to call them "foo(X)" instead of
"new(foo, X)".
On Wed, Apr 9, 2008 at 2:20 AM, Hynek Vychodil <vychodil.hynek@REDACTED> wrote:
> UGH, static functions? Where is benefit to do it? What matter? I don't
> understand.
>
>
>
> On Wed, Apr 9, 2008 at 11:04 AM, Matthew Dempsky <matthew@REDACTED>
> wrote:
>
> >
> >
> >
> > It would be nice to be able to define arbitrary static functions
> > within an abstract module. Right now you can kludge around this by
> > exploiting that local functions named 'new' are always static and
> > write something like
> >
> > new(incr, X) -> X + 1.
> >
> > but it would be nicer to just write
> >
> > -static([incr/1]).
> > incr(X) -> X + 1.
> >
> > Below is a very rudimentary patch that adds support for this syntax.
> > It's basically only enough to compile and run very simple test cases
> > and to demonstrate that implementing this does not seem too difficult.
> > (One problem I'm already aware of is that a static function foo/1 and
> > an instance function foo/0 silently collide without any warning... so
> > don't do that. ;-))
> >
> > Another option would be to make the attribute statement just
> > "-static([incr])." and then all incr functions are defined static, but
> > that seems unnecessarily limiting.
> >
> > If the long-term goal is to have separate namespaces for static and
> > instance functions (e.g., so (Mod:new(...)):module_info() works and
> > returns something meaningful for the module instance), then maybe a
> > syntax that actually decorates individual function definitions would
> > be better?
> >
> > Are there any plans on adding static functions in a future release?
> >
> >
> > --- stdlib/src/erl_parse.yrl.orig 2007-11-27 07:57:32.000000000
> -0800
> > +++ stdlib/src/erl_parse.yrl 2008-04-09 01:25:31.000000000 -0700
> > @@ -627,6 +627,12 @@
> > {attribute,La,export,farity_list(ExpList)};
> > _Other -> error_bad_decl(La, export)
> > end;
> > +build_attribute({atom,La,static}, Val) ->
> > + case Val of
> > + [ExpList] ->
> > + {attribute,La,static,farity_list(ExpList)};
> > + _Other -> error_bad_decl(La, static)
> > + end;
> > build_attribute({atom,La,import}, Val) ->
> > case Val of
> > [Name] ->
> > --- compiler/src/sys_pre_expand.erl.orig 2008-02-05
> 05:37:09.000000000 -0800
> > +++ compiler/src/sys_pre_expand.erl 2008-04-09 01:26:06.000000000
> -0700
> > @@ -38,6 +38,7 @@
> > parameters=undefined, %Module parameters
> > package="", %Module package
> > exports=[], %Exports
> > + statics=[], %Statics
> > imports=[], %Imports
> > mod_imports, %Module Imports
> > compile=[], %Compile flags
> > @@ -109,6 +110,7 @@
> > end,
> > {Fs1,Xs,Ds} = sys_expand_pmod:forms(Fs0, Ps,
> > St0#expand.exports,
> > + St0#expand.statics,
> > St0#expand.defined),
> > St1 = St0#expand{exports=Xs, defined=Ds},
> > {Fs2,St2} = add_instance(Ps, Fs1, St1),
> > @@ -220,6 +222,8 @@
> > package = packages:strip_last(M)};
> > attribute(export, Es, St) ->
> > St#expand{exports=union(from_list(Es), St#expand.exports)};
> > +attribute(static, Ss, St) ->
> > + St#expand{statics=union(from_list(Ss), St#expand.statics)};
> > attribute(import, Is, St) ->
> > import(Is, St);
> > attribute(compile, C, St) when is_list(C) ->
> > --- compiler/src/sys_expand_pmod.erl.orig 2008-02-05
> 05:38:12.000000000 -0800
> > +++ compiler/src/sys_expand_pmod.erl 2008-04-09 01:32:36.000000000
> -0700
> > @@ -25,18 +25,19 @@
> > %% and 'exports'. The automatic 'new/N' function is neither added to the
> > %% definitions nor to the 'exports'/'defines' lists yet.
> >
> > --export([forms/4]).
> > +-export([forms/5]).
> >
> > --record(pmod, {parameters, exports, defined, predef}).
> > +-record(pmod, {parameters, exports, statics, defined, predef}).
> >
> > %% TODO: more abstract handling of predefined/static functions.
> >
> > -forms(Fs0, Ps, Es0, Ds0) ->
> > +forms(Fs0, Ps, Es0, Ss0, Ds0) ->
> > PreDef = [{module_info,0},{module_info,1}],
> > - forms(Fs0, Ps, Es0, Ds0, PreDef).
> > + forms(Fs0, Ps, Es0, Ss0, Ds0, PreDef).
> >
> > -forms(Fs0, Ps, Es0, Ds0, PreDef) ->
> > - St0 = #pmod{parameters=Ps,exports=Es0,defined=Ds0, predef=PreDef},
> > +forms(Fs0, Ps, Es0, Ss0, Ds0, PreDef) ->
> > + St0 = #pmod{parameters=Ps,exports=Es0,statics=Ss0,defined=Ds0,
> > + predef=PreDef},
> > {Fs1, St1} = forms(Fs0, St0),
> > Es1 = update_function_names(Es0, St1),
> > Ds1 = update_function_names(Ds0, St1),
> > @@ -50,15 +51,22 @@
> > [update_function_name(E, St) || E <- Es].
> >
> > update_function_name(E={F,A}, St) when F =/= new ->
> > - case ordsets:is_element(E, St#pmod.predef) of
> > + case ordsets:is_element(E, St#pmod.predef) orelse
> > + ordsets:is_element(E, St#pmod.statics) of
> > true -> E;
> > false -> {F, A + 1}
> > end;
> > update_function_name(E, _St) ->
> > E.
> >
> > -update_forms([{function,L,N,A,Cs}|Fs],St) when N =/= new ->
> > - [{function,L,N,A+1,Cs}|update_forms(Fs,St)];
> > +update_forms([F0={function,L,N,A,Cs}|Fs],St) when N =/= new ->
> > + F = case ordsets:is_element({N,A}, St#pmod.statics) of
> > + true ->
> > + F0;
> > + false ->
> > + {function,L,N,A+1,Cs}
> > + end,
> > + [F|update_forms(Fs,St)];
> > update_forms([F|Fs],St) ->
> > [F|update_forms(Fs,St)];
> > update_forms([],_St) ->
> > @@ -74,9 +82,14 @@
> > {[], St0}.
> >
> > %% Only function definitions are of interest here. State is not updated.
> > -form({function,Line,Name0,Arity0,Clauses0},St) when Name0 =/= new ->
> > - {Name,Arity,Clauses} = function(Name0, Arity0, Clauses0, St),
> > - {{function,Line,Name,Arity,Clauses},St};
> > +form(F = {function,Line,Name0,Arity0,Clauses0},St) when Name0 =/= new ->
> > + case ordsets:is_element({Name0, Arity0}, St#pmod.statics) of
> > + true ->
> > + {F,St};
> > + false ->
> > + {Name,Arity,Clauses} = function(Name0, Arity0, Clauses0, St),
> > + {{function,Line,Name,Arity,Clauses},St}
> > + end;
> > %% Pass anything else through
> > form(F,St) -> {F,St}.
> >
> > @@ -362,7 +375,13 @@
> > expr({call,Lc,{atom,Lf,F},As0},St) ->
> > %% Local function call - needs THIS parameter.
> > As1 = expr_list(As0,St),
> > - {call,Lc,{atom,Lf,F},As1 ++ [{var,0,'THIS'}]};
> > + As2 = case ordsets:is_element({F, length(As1)}, St#pmod.statics) of
> > + true ->
> > + As1;
> > + false ->
> > + As1 ++ [{var,0,'THIS'}]
> > + end,
> > + {call,Lc,{atom,Lf,F},As2};
> > expr({call,Line,F0,As0},St) ->
> > %% Other function call
> > F1 = expr(F0,St),
> > _______________________________________________
> > erlang-questions mailing list
> > erlang-questions@REDACTED
> > http://www.erlang.org/mailman/listinfo/erlang-questions
> >
>
>
>
> --
> --Hynek (Pichi) Vychodil
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