Tutorial ambiguity or mistake re: destructuring & let

[olliebun]

From the tutorial:

You've already seen simple let bindings, but let is a little fancier than you've been led to believe. It, too, supports destructuring patterns. For example, you can write this to extract the fields from a tuple, introducing two variables at once: a and b.

let (a, b) = get_tuple_of_two_ints();

Let bindings only work with irrefutable patterns: that is, patterns that can never fail to match. This excludes let from matching literals and most enum variants.

(emphasis mine)

This code compiles and behaves as expected:

let (a, b) = (1,2);

Have not included a pull request, as I'm not sure what the meaning of the passage is otherwise.

[glaebhoerl]

That does, but this doesn't:

let (a, 2) = (1, 2);

which is the intended meaning.

Can you suggest a phrasing which would've been unambiguous for you?

[jhasse]

How about simply removing the last sentence? That let (a, 2) = (1, 2) doesn't work shouldn't need explaining IMHO.

[olliebun]

Tricky - this seems to suggest that you can destructure literals with let bindings, just that you can't do so into a pattern that exists in a match. Is that right?

[glaebhoerl]

Hmm? The thing being matched (on the RHS of let, or directly following match) does not matter at all. What matters is that in a let, on the LHS, you can only have a single pattern which must match any possible value of the type. If you need more than one pattern to cover all the cases, you need to use a match.

[pnkfelix]

part of #11755

[steveklabnik]

I've made a PR to improve this. Thoughts?

[olliebun]

Yep that makes sense.