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Remove remark about poor code style #37503

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Nov 12, 2016
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Remove remark about poor code style #37503

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1b39c0a
Remove remark about poor code style
nwin Oct 31, 2016
5cf07f1
Update patch with example.
nwin Nov 4, 2016
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22 changes: 1 addition & 21 deletions src/doc/book/traits.md
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Expand Up @@ -243,27 +243,7 @@ to know more about [operator traits][operators-and-overloading].
# Rules for implementing traits

So far, we’ve only added trait implementations to structs, but you can
implement a trait for any type. So technically, we _could_ implement `HasArea`
for `i32`:

```rust
trait HasArea {
fn area(&self) -> f64;
}

impl HasArea for i32 {
fn area(&self) -> f64 {
println!("this is silly");

*self as f64
}
}

5.area();
```

It is considered poor style to implement methods on such primitive types, even
though it is possible.
implement a trait for any type such as `i32`.
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leave the example in I guess?

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Maybe. Then I would suggest to change the implementation to

impl HasArea for i32 {
    fn area(&self) -> f64 {
        println!("this is silly");

        0.0
    }
}

to depict the silliness of calculating the area of a scalar.

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How about .squared()?

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That would actually be bad style (imho). One cannot implement a meaningful area for i32, only for the newtype struct Square(i32). This is why I wanted to remove the example altogether because that possibly lengthy discussion is out of scope of that particular paragraph.

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@nwin Can you suggest an alternative non-silly example that we could put here?

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We could make up a trait like Complex and output the real and imaginary part in two methods.

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I've just come up with a better idea.

trait ApproxEqual {
    fn approx_equal(&self, other: &Self);
}
impl ApproxEqual for f64 {
    fn approx_equal(&self, other: &Self) {
        // Impementation to be improved for the actual example
        // Only valid for numbers close to 1.0
        (self - other).abs() < ::std::f64::EPSILON 
}


This may seem like the Wild West, but there are two restrictions around
implementing traits that prevent this from getting out of hand. The first is
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