Support streaming and unit symbols for Eigen - #736
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I was working on an Eigen example, and found that some basic stuff people would expect wasn't working yet. So I added tests and fixed it. On streaming: we've been using the "unary plus" for a long time in order to promote small integers that alias to `char`. The problem is that not every rep necessarily supports unary plus. Therefore, we guard it behind a utility called as `promote_for_streaming(x, 0)`, and SFINAE out the unary plus when it doesn't exist. On unit symbols: apparently, we had been constraining them to arithmetic types only. Well, we have a canonical trait for what's a valid rep: `IsValidRep`. Even if it's not fully fleshed out yet, it's the authoritative answer. So now we just use that consistently.
chiphogg
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August 22, 2026 02:59
hoffbrinkle
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Aug 24, 2026
| // the operand, which will then match an appropriate << operator that will | ||
| // output the integer representation. | ||
| out << +q.in(U{}) << " " << unit_label(U{}); | ||
| out << detail::promote_for_streaming(q.in(U{}), 0) << " " << unit_label(U{}); |
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It's part of the detail API, so not critical, but the 0 for the second parameter is not-intuitive.
And really, the only type we're really worried about is the single byte integers which happen to be a char underneath, and char has this unfortunate ambiguity. I suppose there's no good way to select on that?
Co-authored-by: Michael Hordijk <hordijk@aurora.tech>
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I was working on an Eigen example, and found that some basic stuff
people would expect wasn't working yet. So I added tests and fixed it.
On streaming: we've been using the "unary plus" for a long time in order
to promote small integers that alias to
char. The problem is that notevery rep necessarily supports unary plus. Therefore, we guard it
behind a utility called as
promote_for_streaming(x, 0), and SFINAE outthe unary plus when it doesn't exist.
On unit symbols: apparently, we had been constraining them to arithmetic
types only. Well, we have a canonical trait for what's a valid rep:
IsValidRep. Even if it's not fully fleshed out yet, it's theauthoritative answer. So now we just use that consistently.