src/tools/clippy/src/docs/redundant_pattern_matching.txt

   1 ### What it does
   2 Lint for redundant pattern matching over `Result`, `Option`,
   3 `std::task::Poll` or `std::net::IpAddr`
   4
   5 ### Why is this bad?
   6 It's more concise and clear to just use the proper
   7 utility function
   8
   9 ### Known problems
  10 This will change the drop order for the matched type. Both `if let` and
  11 `while let` will drop the value at the end of the block, both `if` and `while` will drop the
  12 value before entering the block. For most types this change will not matter, but for a few
  13 types this will not be an acceptable change (e.g. locks). See the
  14 [reference](https://doc.rust-lang.org/reference/destructors.html#drop-scopes) for more about
  15 drop order.
  16
  17 ### Example
  18 ```
  19 if let Ok(_) = Ok::<i32, i32>(42) {}
  20 if let Err(_) = Err::<i32, i32>(42) {}
  21 if let None = None::<()> {}
  22 if let Some(_) = Some(42) {}
  23 if let Poll::Pending = Poll::Pending::<()> {}
  24 if let Poll::Ready(_) = Poll::Ready(42) {}
  25 if let IpAddr::V4(_) = IpAddr::V4(Ipv4Addr::LOCALHOST) {}
  26 if let IpAddr::V6(_) = IpAddr::V6(Ipv6Addr::LOCALHOST) {}
  27 match Ok::<i32, i32>(42) {
  28     Ok(_) => true,
  29     Err(_) => false,
  30 };
  31 ```
  32
  33 The more idiomatic use would be:
  34
  35 ```
  36 if Ok::<i32, i32>(42).is_ok() {}
  37 if Err::<i32, i32>(42).is_err() {}
  38 if None::<()>.is_none() {}
  39 if Some(42).is_some() {}
  40 if Poll::Pending::<()>.is_pending() {}
  41 if Poll::Ready(42).is_ready() {}
  42 if IpAddr::V4(Ipv4Addr::LOCALHOST).is_ipv4() {}
  43 if IpAddr::V6(Ipv6Addr::LOCALHOST).is_ipv6() {}
  44 Ok::<i32, i32>(42).is_ok();
  45 ```