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libcore: Implement an Equiv trait and use it on hashmaps. #5234

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libcore: Implement an Equiv trait and use it on hashmaps. #5234

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@pcwalton pcwalton commented Mar 5, 2013

@pcwalton
libsyntax: Separate multiple inherited traits with +
6d4ed52
@pcwalton
librustc: Fix silly bug in AST conversion for const vstores. rs=bugfix
c407549 
Means that we'll need another snapshot to rid the language of `[const T]`.
@pcwalton
libcore: Implement an Equiv trait and use it on hashmaps.
2fa2ad5 
7.3x speedup in string map search speed on a microbenchmark of pure hashmap
searching against a constant string, due to the lack of allocations.

I ran into a few snags.

1. The way the coherence check is set up, I can't implement `Equiv<@str>` and
   `Equiv<~str>` for `&str` simultaneously.

2. I wanted to implement `Equiv<T>` for all `T:Eq` (i.e. every type can be
   compared to itself if it implements `Eq`), but the coherence check didn't
   like that either.

3. I couldn't add this to the `Map` trait because `LinearMap` needs special
   handling for its `Q` type parameter: it must not only implement `Equiv<T>`
   but also `Hash` and `Eq`.

4. `find_equiv(&&"foo")` doesn't parse, because of the double ampersand. It has
   to be written `find_equiv(& &"foo")`. We can probably just fix this.

Nevertheless, this is a huge win; it should address a major source of
performance problems, including the one here:

http://maniagnosis.crsr.net/2013/02/creating-letterpress-cheating-program.html
bors added a commit that referenced this pull request Mar 5, 2013
@bors
auto merge of #5234 : pcwalton/rust/equiv, r=pcwalton
dec599f 
r? @nikomatsakis
@bors bors closed this Mar 5, 2013
flip1995 pushed a commit to flip1995/rust that referenced this pull request Apr 8, 2021
@bors
Auto merge of rust-lang#6463 - xFrednet:5234-shared-code-in-if-blocks…
d91da40 
…, r=phansch

New Lint: `branches_sharing_code`

This lint checks if all `if`-blocks contain some statements that are the same and can be moved out of the blocks to prevent code duplication. Here is an example:

```rust
let _ = if ... {
    println!("Start"); // <-- Lint for code duplication
    let _a = 99;
    println!("End"); // <-- Lint for code duplication
    false
} else {
    println!("Start");
    let _b = 17;
    println!("End");
    false
};
```

This could be written as:

```rust
println!("Start");

let _ = if ... {
    let _a = 99;
    false
} else {
    let _b = 17;
    false
};

println!("End");
```

---

This lint will get masked by the `IF_SAME_THEN_ELSE` lint. I think it makes more sense to only emit one lint per if block. This means that the folloing example:

```rust
if ... {
    let _a = 17;
} else {
    let _a = 17;
}
```

Will only trigger the `IF_SAME_THEN_ELSE` lint and not the `SHARED_CODE_IN_IF_BLOCKS` lint.

---

closes: rust-lang#5234

changelog: Added a new lint: `branches_sharing_code`

And hello to the one that is writing the changelog for this release :D
calebcartwright pushed a commit to calebcartwright/rust that referenced this pull request Jun 20, 2023
@davidBar-On
Fix rust-lang#5234 - handling of empty code block (rust-lang#5601)
b08130c
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2 participants
@pcwalton @bors