WIP: Patterns chapter #284
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- Added the chapter about patterns, with some explanations and the grammar. - Had to move some documentation about patterns from the `match` section. - Removed the bit about the new syntax of inclusive pattern ranges (a..=b), since it is not stable nor in the process of being stabilized.
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Thanks so much for this! It looks great. I've left some comments from going through this.
Match default binding modes (#280, rust-lang/rust#42640) are stable on nightly now, but I'm fine with merging this without them.
| parameters | ||
| * [`match` expressions](expressions.html#match-expressions) | ||
| * [`if let` expressions](expressions.html#if-let-expressions) | ||
| * [`while let` expressions](expressions.html#while-let-loops) |
| when creating such values. When destructing a data structure with named (but | ||
| not numbered) fields, it is allowed to write `fieldname` as a shorthand for | ||
| `fieldname: fieldname`. In a pattern whose head expression has a `struct`, | ||
| `enum` or `tupl` type, a placeholder (`_`) stands for a *single* data field, |
| 0 ..= <u32 as MaxValue>::MAX => "fits in a u32", | ||
| _ => "too big", | ||
| }); | ||
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| Qualified path patterns can only refer to associated constants. | ||
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| Path patterns are irrefutable when they refer to constants or structs. | ||
| They are refutable when the refer to enum variants. |
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They're irrefutable if the enum only has one variant.
| > | _QualifiedPathForExpression_ | ||
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| _Path patterns_ are patterns that refer either to constant values or | ||
| to structs or enum variants that have no fields. |
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unit structs and unit variants, struct A {} doesn't allow A as a pattern.
| > **<sup>Syntax</sup>** | ||
| > _IdentifierPattern_ : | ||
| > `mut`<sup>?</sup> IDENTIFIER (`@` [_Pattern_] ) <sup>?</sup> | ||
| > | `ref` `mut`<sup>?</sup> IDENTIFIER (`@` [_Pattern_] ) <sup>?</sup> |
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Why isn't this `ref` ? `mut` ? ... ?
| } | ||
| ``` | ||
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| in the first match expression, the value is copied (or moved). In the second match, |
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'In'. I think that code blocks count as the end of a sentence.
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| Reference patterns are always irrefutable. | ||
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| ## Identifier patterns |
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Can this section be moved up to before Wildcard pattern?
| > _WildcardPattern_ : | ||
| > `_` | ||
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| The _wildcard pattern_ matches any value. It is used to ignore values when they don't |
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Can you add a sentence to this section saying something like "unlike identifier patterns, it does not copy, move or borrow the value it matches."
| @@ -60,6 +60,8 @@ | |||
| - [Match expressions](expressions/match-expr.md) | |||
| - [Return expressions](expressions/return-expr.md) | |||
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| - [Patterns](patterns.md) | |||
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@Havvy should this be under Statements and expressions?
| _ => { /* this wildcard is required, since we don't know length statically */ } | ||
| } | ||
| ``` | ||
| A range pattern may not be a sub-range of another range pattern inside the same `match`. |
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This doesn't seem to be true; https://play.rust-lang.org/?gist=49813df7725fc36a71959a136841ce14&version=nightly shows only a warning.
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This also fixes #300. |
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Also #301. |
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@brauliobz Are you still working on this? |
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I contacted Bráulio and he said that he hasn't been able to work on this lately. If nobody minds, I'm going to try to finish it off. |
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Closing in favor of #419 |
matchexpression section.Removed the bit about the new syntax of inclusive pattern ranges (a..=b),since it is not stable nor in the process of being stabilized.
Closes #83, closes #300, #301.