Avoid generating lots of small temporary functions.

[FeepingCreature]

• Move destructor lambda into global scope (allow instance reuse)
• Move stride template into global scope (allow instance reuse)
• getValues yields a string of an argument list instead of a value tuple.

Effects:

• slightly slower in normal operation
• enormously faster in degenerate cases (large number of types, -O -inline) due to avoiding overloading the inliner
• smaller object file size.

To reproduce the degenerate case, try with this test program (remember -O -inline):

module test;

import std;
import sumtype;

struct S(int i) { }

void main() {
    alias mega = SumType!(staticMap!(S, aliasSeqOf!(15.iota)));
    mega.init == mega.init;
}

Adjust the iota to make things slower. Note that we have a 21-type SumType in practice - this is not academic! If you set iota to 21, then in the stock 1.0.0 version the optimizer will run for at least five minutes. (At least that's where I gave up.)

[pbackus]

The changes to getValue fail when compiling with -betterC. This should have been caught automatically, but there was a typo in my Github Actions workflow (now fixed) preventing tests from being run on PRs. You can test your changes locally with test-betterc.sh.

[FeepingCreature]

The lack of format! and join really hurts, even at compiletime. Seems to work now though.

[pbackus]

Tagged as v1.0.1. Thanks a lot!

[pbackus]

This PR introduced a regression (#65).