DIP 1027---String Interpolation---Format Assessment

[Steven Schveighoffer]

On 2/24/20 12:31 PM, H. S. Teoh wrote:
> On Mon, Feb 24, 2020 at 10:41:16AM -0500, Steven Schveighoffer via Digitalmars-d-announce wrote:
> [...]
>> I will also note that we did something very similar with
>> switch(string), where prior to this the compiler did all the "heavy
>> lifting" of generating the code to convert strings into integers. Now
>> it's done via a template which accepts all the strings as parameters.
>> I don't think it was a bad change, and I'm sure it increased compile
>> times and compiler memory usage.
> 
> No kidding, at one point it was making Phobos uncompilable except for
> machines with huge gobs of RAM, because std.datetime had this gigantic
> switch statement over, like, *every* locale name that exists in the
> world, and it was causing a gigantic explosion of template bloat. I
> think the solution that was eventually adopted was to replace that
> switch with something else, which is not altogether a bad thing I
> suppose, but still, it does put to question the practicality of having a
> template generate code for a switch statement with >1000 string items.

The solution was to forward templates over a certain number of string 
elements to a single runtime function with an array created from the 
tuple list (which is a minimal wrapper) instead of a binary search via 
unrolled templates: 
https://github.com/dlang/druntime/blob/87bf88ba88d2926d7a470b5e126e0a5b1a1e266f/src/core/internal/switch_.d#L60-L73. 
It's unfortunate we even have to use CTFE to generate the immutable strings.

I wouldn't imagine a much different approach for this proposal as well 
-- convert to something useful at runtime and then call a runtime-only 
implementation.

As I said before, if we can make it so such "wrappers" are just 
forwarders, it would make the resulting code less bloated, and probably 
save on memory as well.

-Steve