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Apr 19, 2015
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doc: improve/fix 'let' FAQ #24554

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9 changes: 5 additions & 4 deletions src/doc/complement-design-faq.md
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Expand Up @@ -165,12 +165,13 @@ particularly easy to read.

## Why is `let` used to introduce variables?

We don't use the term "variable", instead, we use "variable bindings". The
simplest way for binding is the `let` syntax, other ways including `if let`,
`while let` and `match`. Bindings also exist in function arguments positions.
Instead of the term "variable", we use "variable bindings". The
simplest way for creating a binding is by using the `let` syntax.
Other ways include `if let`, `while let`, and `match`. Bindings also
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One thing is missing here: for-in also do pattern matching.

edit: fix typo

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This has now be merged, so you can create a separate PR.

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What do you think about "Other ways include if let, while let, match and for ... in. "?

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While doing this PR, I was actually thinking maybe it should a bullet list:

Other ways of creating bindings:

  • if let
  • while let
  • ...

BTW, for item in items is a nice catch... I forgot about it.

exist in function argument positions.

Bindings always happen in pattern matching positions, and it's also Rust's way
to declare mutability. One can also redeclare mutability of a binding in
to declare mutability. One can also re-declare mutability of a binding in
pattern matching. This is useful to avoid unnecessary `mut` annotations. An
interesting historical note is that Rust comes, syntactically, most closely
from ML, which also uses `let` to introduce bindings.
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