Soup up 'method syntax' chapter of the Book #21108
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r? @pcwalton (rust_highfive has picked a reviewer for you, use r? to override) |
| ## Chaining method calls | ||
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| So, now we know how to call a method, such as `foo.bar()`. But what about our | ||
| original example, `foo.bar().baz()`? This is called 'method chaning', and we |
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Thanks @thommay |
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Sorry that was a bit of a drive-by review :) |
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No sorries needed, I appreciate it very much! |
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| We just say we're returning a `Circle`. With this, we can grow a new circle | ||
| that's twice as big as the old one. But what if we didn't want to make a new | ||
| Circle, but change the old one? There's a pattern where this is commonly used: |
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This sentence seems a little odd starting with "But" and then also having a conjunction "but"
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Yeah, the second one should be 'and'
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| impl Circle { | ||
| fn x(&mut self, x: f64) -> &mut Circle { |
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Wouldn't it be more convenient for the caller if the method takes and returns self by value?
eg: fn x(mut self, x: f64) -> Circle
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If you're referring to the "Advanced Builder Pattern" section then it's missing.
If not then I don't know what I missed.
let circle: Circle = Circle::new().radius(5.0).coordinate(10.0); // Methods are by-valueseems a lot more usable to me than
let mut circle_builder = CircleBuilder::new();
circle_builder.radius(5.0).coordinate(10.0); // Methods are by-reference
let circle: Circle = circle_builder.finalise();Edit: Or even the simplified case without an extra builder type:
let mut circle: Circle = Circle::new();
circle.radius(5.0).coordinate(10.0); // Methods are by-referenceThere was a problem hiding this comment.
Yeah, I was, since the consuming form was what I was thinking of.
I think you're right, after seeing that code. Will change.
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Note that builders by reference are currently preferred, but there are definitely tradeoffs both ways. This is meant to be a fairly trivial example, so the by-reference may not make much sense, but I've found that by-reference is almost always what you want for some serious configuration going on as you don't have to move it around all over the place.
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I wish that we had pubished the guidelines officially so I could link to them from here...
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I did some significant editing here. What do you think @alexcrichton ? |
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| let c = cb.coordinate(10.0) | ||
| .radius(5.0); | ||
| .finalize(); |
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Does this compile? The finalize method consumes the builder but the previous methods are just returning references (and the builder doesn't have derive(Copy))
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i ran rustdoc --test and it passed...
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It looks like there's another error as well (the semicolon after the call to radius)
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@alexcrichton addressed. |
| ``` | ||
| # struct Circle; | ||
| # impl Circle { | ||
| fn finalize(self) -> Circle { |
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I think this (and the below paragraph need to be udpated)
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Just a small nit, otherwise r=me, thanks! |
Fixes #16969