Use const functions where possible

[richardpringle]

I just used clippy for this. I actually assume that you will not want the brunt of this change but I figured it was easier to make the change everywhere then simply pick the ones you deem acceptable (if any).

I definitey think some of the constructors should be const.

Thanks in advance!

[VictorKoenders]

Looks good to me.

Out of pure interest, can you check if this actually improves any of the benchmarks?

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (ff7a45a) 57.24% compared to head (4a77a75) 57.24%.

Files	Patch %	Lines
src/error.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            trunk     #684   +/-   ##
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  Coverage   57.24%   57.24%           
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  Files          51       51           
  Lines        4350     4350           
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  Hits         2490     2490           
  Misses       1860     1860           

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[richardpringle]

Looks good to me.

Out of pure interest, can you check if this actually improves any of the benchmarks?

I'm not quite sure I understand what you're asking. const shouldn't change the behaviour at all, it will only make those functions available in const context. In order to improve a benchmark, you would have to change the code at the call-site.

You should also be aware that removing const from a pub const function is a breaking change. Given the extensive use of the builder-pattern, this shouldn't be a concern, though.