I get a string from HTTP request and I need to process a member of this name of an object. I would like to use __traits(getMember) for that, but of course it doesn't work with runtime parameters. So what I ended up with is:

foreach( s; __traits(derivedMembers, typeof(obj))) {
  if (s == name) ...
}

Of course this looks suboptimal as I run the loop until I find a member matching the name. Is there any better way to do this?

-- 
Marek Janukowicz

On 2013-08-21 10:10, Marek Janukowicz wrote:
> I get a string from HTTP request and I need to process a member of this name
> of an object. I would like to use __traits(getMember) for that, but of
> course it doesn't work with runtime parameters. So what I ended up with is:
>
> foreach( s; __traits(derivedMembers, typeof(obj))) {
>    if (s == name) ...
> }
>
> Of course this looks suboptimal as I run the loop until I find a member
> matching the name. Is there any better way to do this?

I don't think so. Unless you build a set or associative array at compile time with all the members of a given type.

-- 
/Jacob Carlborg

On Wednesday, 21 August 2013 at 12:03:38 UTC, Jacob Carlborg wrote:
> Unless you build a set or associative array at compile time with all the members of a given type.

Or build a string with a switch() { case "member1": member1(); break; case "mem2": mem2(); }

then mix that in and hope the compiler optimizes the switch.

On Wednesday, 21 August 2013 at 08:08:56 UTC, Marek Janukowicz wrote:
> I get a string from HTTP request and I need to process a member of this name
> of an object. I would like to use __traits(getMember) for that, but of
> course it doesn't work with runtime parameters. So what I ended up with is:
>
> foreach( s; __traits(derivedMembers, typeof(obj))) {
>   if (s == name) ...
> }
>
> Of course this looks suboptimal as I run the loop until I find a member
> matching the name. Is there any better way to do this?

I wrote something for this a while back for loading config files:

https://github.com/John-Colvin/ES/blob/master/JCutils.d#L195

You'll need everything from that line downwards.

On Wednesday, 21 August 2013 at 13:00:40 UTC, John Colvin wrote:
> On Wednesday, 21 August 2013 at 08:08:56 UTC, Marek Janukowicz wrote:
>> I get a string from HTTP request and I need to process a member of this name
>> of an object. I would like to use __traits(getMember) for that, but of
>> course it doesn't work with runtime parameters. So what I ended up with is:
>>
>> foreach( s; __traits(derivedMembers, typeof(obj))) {
>>  if (s == name) ...
>> }
>>
>> Of course this looks suboptimal as I run the loop until I find a member
>> matching the name. Is there any better way to do this?
>
> I wrote something for this a while back for loading config files:
>
> https://github.com/John-Colvin/ES/blob/master/JCutils.d#L195
>
> You'll need everything from that line downwards.

struct A
{
    int a,b,c,d,e,f,g,h,i,j,k;
}

A a;
auto byString = string_access!int(a);

string name = //some RT val
int val = //some RT val

byString[name] = val;

On Wed, Aug 21, 2013 at 10:10:29AM +0200, Marek Janukowicz wrote:
> I get a string from HTTP request and I need to process a member of this name of an object. I would like to use __traits(getMember) for that, but of course it doesn't work with runtime parameters. So what I ended up with is:
> 
> foreach( s; __traits(derivedMembers, typeof(obj))) {
>   if (s == name) ...
> }
> 
> Of course this looks suboptimal as I run the loop until I find a member matching the name. Is there any better way to do this?
[...]

Maybe you could put this foreach inside a static this() (i.e. module
ctor) and have it initialize a hash table of members at startup time?
Then you can use the hash to look things up quickly.


T

-- 
I'm still trying to find a pun for "punishment"...