CT filtering of class members

Simen Kjærås simen.kjaras at gmail.com
Sun Aug 11 16:32:20 UTC 2019

On Sunday, 11 August 2019 at 15:27:54 UTC, Sjoerd Nijboer wrote:
> The following snippet doesn't compile
> I am trying to reflect on a class and only do an operation with 
> all member functions of a class.
> But I can't seem to use a filter to only get the member 
> functions out of a type T.
> I understand that there are two errors in my snippet.
> 1) It cannot mixin a `name` because it is a variable from the 
> lambda that `filter()` is using.
> 2) members.filter!(name => !ctorAndDtor.canFind(name)) does not 
> filter on symbols defined in ctorAndDtor
> How can I fix these problems and return all member functions 
> whitout ctor and dtor of a type T?

This is classic D mix of compile-time and compile-time (no typo). 
I suggest reading H.S. Teoh's text on the topic: 

Now, as for what can actually be done: you should probably use 
std.meta.Filter (https://dlang.org/library/std/meta/filter.html) 
to filter the members list. This will require you to define a 
template to operate on each element. Something like this:

     import std.meta : Filter;
     import std.traits : isFunction;
     import std.algorithm.searching : canFind;

     enum isNonspecialMemberFunction(string name) = 
!ctorAndDtor.canFind(name) &&
isFunction!(__traits(getMember, T, name));
     enum memberFunctions = Filter!(isNonspecialMemberFunction, 
__traits(derivedMembers, T));

Filter operates on AliasSeqs, not arrays. That's why I restated 
the __traits(derivedMembers, T) part, but this could just as 
easily be done by changing this line:

     enum members = [__traits(derivedMembers, T)];


     alias members = __traits(derivedMembers, T);


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