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for std::decay fix, anchor and cross-reference tuple-cat fix more accurately

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slymz
2020-05-06 18:27:35 -04:00
parent 2e6c2abcde
commit 742980e533
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doc/mp11/examples.adoc
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@ -264,6 +264,7 @@ Long story short, we need `std::move(tp)` in `tuple_cat_` to make `tp` an rvalue
return R{ std::get<Ks::value>(std::get<Is::value>(std::move(tp)))... };
}
[[fixing-tuple-cat-const-issue]]
Next, `const`-qualified tuples. The issue here is that we're stripping references from the input tuples, but not
`const`. As a result, we're trying to manipulate types such as `tuple<int> const` with Mp11 algorithms, and these
types do not fit the list concept. We just need to strip qualifiers as well, by defining the useful `remove_cv_ref`
@ -424,7 +425,7 @@ With `Qret` in hand, a `variant` of the possible return types is just a matter o
Why does this work? `mp_product<F, L1<T1...>, L2<T2...>, ..., Ln<Tn...>>` returns `L1<F<U1, U2, ..., Un>, ...>`, where `Ui` traverse all
possible combinations of list values. Since in our case all `Li` are `std::variant`, the result will also be `std::variant`. (`mp_product_q` is
the same as `mp_product`, but for quoted metafunctions such as our `Qret<F>` or `Qret_F`.) We needed to use `std::decay_t` for precisely the
same reason as in the link:#fixing-tuple_cat[Fixing tuple_cat example], where `std::decay_t` is an equivalent alternative to `remove_cv_ref`.
same reason as in the <<fixing-tuple-cat-const-issue,Fixing tuple_cat example>>, where `std::decay_t` is an equivalent alternative to `remove_cv_ref`.
One more step remains. Suppose that, as above, we're passing two variants of type `std::variant<short, int, float>` and `F` is