Re: [Boost-users] [Unordered] [Multi-Index] Set lookup from something else than key_type

Subject: Re: [Boost-users] [Unordered] [Multi-Index] Set lookup from something else than key_type
From: Dominique Devienne (ddevienne_at_[hidden])
Date: 2009-09-02 14:56:37

On Wed, Sep 2, 2009 at 7:23 AM, Daniel James<daniel_james_at_[hidden]> wrote:
>>  template<
>>   typename CompatibleKey,typename CompatibleHash,typename CompatiblePred
>>  >
>>  iterator find(
>>   const CompatibleKey& k,
>>   const CompatibleHash& hash,const CompatiblePred& eq)const;
>>
>> which is a pure extension without backwards compatibility problems. This
>> is seemingly what Boost.Intrusive is doing.
>
> Yes, I think I'll add that to the new version which should be released
> in 1.41 or 1.42.

This would indeed cleanly solve my problem.

FTR, I tend to lean on Joaquín's side of the argument. If the provided
explicit Hash/Pred template parameters of unordered_set do provide overloads
for compatible keys, then it's "by design" that find() should use them.

If previous code that was relying on an implicit conversion to key_type
starts using added overload on Pred/Hash, this simply means that the
container designer made this choice explicitly, and I don't see why that
a bad thing. After all the overloads were added for avoiding the key
creation, which is exactly what I was trying to do here.

In Joaquín's proposal, all clients using find() implicitly start using the
optimized find() avoiding the key_type conversion once the container
is modified and the client code is recompiled. No code necessary.

That's a good thing to me. But that's just me ;) --DD