Can we deprecate "D-style Variadic Functions"
Shammah Chancellor via Digitalmars-d
digitalmars-d at puremagic.com
Fri Mar 27 07:24:47 PDT 2015
On 2015-03-26 01:04:03 +0000, Freddy said:
> On Thursday, 26 March 2015 at 00:11:05 UTC, Dicebot wrote:
>> On Wednesday, 25 March 2015 at 22:12:04 UTC, Freddy wrote:
>>> "D-style Variadic Functions" found here:http://dlang.org/function.html
>>> seem entirely out classed by Variadic Function Templates. Can we
>>> deprecate them?
>>
>> Those are two different concepts with different trade-offs. Using
>> variadic templates adds template bloat. Using D-style variadics
>> requires RTTI (and small overhead for it). It is up to
>> library/application writer to decide what is best in his case.
>
> My ploblem is that Variadic Function shouldn't be builtin the language.
> They are rarely need and can be abstracted into a library. Something
> like this:
> ```
> import core.stdc.stdlib: alloca;
> import std.stdio;
> template VariadicFunction(alias Imp){
> auto VariadicFunction(T...)(T args){
> enum size=T.length * TypeInfo.sizeof;
> auto rtti=cast(TypeInfo[])(alloca(size)[0..size]);
> foreach(i,type;T){
> rtti[i]=typeid(type);
> }
> //auto data=&args; bug? doesn't work
> void* data;
> {
> size_t datasize;//T.sizeof doesn't work
> foreach(type;T){
> datasize+=type.sizeof;
> }
> data=alloca(datasize);
> size_t inc;
> foreach(v;args){
> *cast(typeof(v)*)(data+inc)=v;
> inc+=v.sizeof;
> }
> }
> Imp(data,rtti);
> }
> }
>
> private void rtVariadicImp(void* vars,scope const TypeInfo[] rtinfo){
> writeln(*cast(int*)vars);
> writeln(rtinfo);
> }
>
> alias rtVariadic=VariadicFunction!(rtVariadicImp);
>
> void main(){
> rtVariadic(1,'a');
> }
> ```
I disagree, and your example does not get rid of the template bloat.
That does in fact instantiate a template for every set of argument
types.
-Shammah
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