chore(sumtype): avoid quadratic memory complexity on opEquals

[ljmf00]

Signed-off-by: Luís Ferreira [email protected]

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Due to match template being quadratic/exponential in terms of memory complexity, (-vtemplate reports a rediculous amount of templates) using opEquals will generate a lot of unnecessary template instances. Removing match here to prevent that.

[dlang-bot]

Thanks for your pull request, @ljmf00!

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[pbackus]

I would much, much rather improve match itself than avoid using it. Duplication like this increases maintenance burden and risks introducing bugs (in fact, I think it has introduced one already).

One simple optimization we can do is to replace the lambda handler in opEquals with a global function, so that instantiations will be shared between different SumType instances. This will also cut down on instantiations of canMatch.

[RazvanN7]

@ljmf00 The style checker fails:

Enforce whitespace before opening parenthesis
--
  | grep -nrE "\<(for\|foreach\|foreach_reverse\|if\|while\|switch\|catch\|version)\(" $(find etc std -name '*.d') ; test $? -eq 1
  | std/sumtype.d:717:            final switch(tag)
  | std/sumtype.d:719:                static foreach(idx, T; Types)
  | std/sumtype.d:724:                            static foreach(ridx, U; typeof(rhs).Types)
  | make: *** [posix.mak:587: style_lint_shellcmds] Error 1

• Mind @pbackus 's comment.