String concatenation tweaks

Aleksey Shipilev aleksey.shipilev at
Thu Jun 4 13:41:48 UTC 2015

On 06/04/2015 03:56 PM, Aleksey Shipilev wrote:
> On 06/04/2015 03:35 PM, Maurizio Cimadamore wrote:
>> Well, yes - but adding a new indy is not something that comes for free.
>> We are currently fighting to get specialization to work correctly with
>> lambdas, and it turns out that having an indy, as Brian said, is like
>> having an entirely new bytecode - so, for every new 'officially
>> supported' bootstrap that we add, we will need to find ways to make that
>> work with whatever new feature XYZ we could come up in the future.
> Yes. This is why we better spend time figuring if the proposed indy
> interface is enough/future-proof.

In other words, we do indeed introducing something similar to a new
bytecode, a long missing "string concat". Would you argue we need to
continue band-aiding the impedance between JLS allowing String concat
and JVMS not having the appropriate facilities for it -- and forcing the
VM implementations to recognize all these translated forms? Indy allows
us to overcome this impedance with one leap.

This also opens up the way into using the (potentially unsafe) private
APIs for concat on VM side, like fixed-length string builders proposed
in this thread. Doing the same on javac side would mean these private
APIs have to be leaked into public.


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