Method cascades

[dharmatech]

Consider method cascades for Rust.

[mstewartgallus]

Is it possible to do this with a macro? It could have a syntax like:

 let address = with! (
     mut it = getAddress();
     setStreet(“Elm”, “13a”)
     setCity(“London”)
     setProvince(“Airstrip One”)
     setState(“Oceania”)
     setZip(66666, 6666)
 );

And that would desugar to something like

 let address = {
     let mut it = getAddress ();
     it.setStreet(“Elm”, “13a”);
     it.setCity(“London”);
     it.setProvince“Airstrip One”);
     it.setState("Oceania”);
.    it.setZip(66666, 6666);
     it
 };

Something along these lines could be useful to implement.

[metajack]

This is like Clojure's doto it seems. I'm not sure it's a good idea to assign to it every time. That would basically mean the underlying calls would need to be chainable, which is not always true.

[bstrie]

It's a neat concept, and I think I actually prefer the look of it to method chaining, but I'm not sure if it's really necessary for Rust.

[emberian]

This would be pretty cool indeed, as a syntax extension.

[Aatch]

If anybody is still interested in this, an official RFC should be filed. https://github.com/rust-lang/rfcs/blob/master/active/0001-rfc-process.md

[ariasuni]

@huonw has implemented cascade operator with a macro that can be used as follow:

let value = cascade!(Foo::new()
                     .. add_to_y(2.0)
                     .. x = 2
                     .. double_x()
                     .. z = "bar".to_strbuf());

I think it’s a great addition to the language compared to the quantity of code to merge, so please re-open.

[bstrie]

Before adding such a macro by default, I would like someone to demonstrate places in real Rust code that could benefit from it. An operator that is useful according to Dart's idioms is not automatically useful in Rust. Until then, this issue should not be re-opened.

[emberian]

I've used a similar macro called with (emulating VB.NET's with
statement), but it was only for a toy -- I found no uses for it in real
code.

On Sun, May 18, 2014 at 7:24 PM, Ben Striegel notifications@github.comwrote:

Before adding such a macro by default, I would like someone to demonstrate
places in real Rust code that could benefit from it. An operator that is
useful according to Dart's idioms is not automatically useful in Rust.
Until then, this issue should not be re-opened.

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[emberian]

(Especially since we have functional record update)

On Sun, May 18, 2014 at 7:35 PM, Corey Richardson corey@octayn.net wrote:

I've used a similar macro called with (emulating VB.NET's with
statement), but it was only for a toy -- I found no uses for it in real
code.

On Sun, May 18, 2014 at 7:24 PM, Ben Striegel notifications@github.comwrote:

Before adding such a macro by default, I would like someone to
demonstrate places in real Rust code that could benefit from it. An
operator that is useful according to Dart's idioms is not automatically
useful in Rust. Until then, this issue should not be re-opened.

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[ariasuni]

I don’t link to lines where the use of cascade operator would me more verbose than without it.

https://github.com/mozilla/rust/blob/master/src/librustc/back/archive.rs#L59
https://github.com/mozilla/rust/blob/master/src/librustc/back/rpath.rs#L184
https://github.com/mozilla/rust/blob/master/src/librustc/middle/liveness.rs#L827
https://github.com/mozilla/rust/blob/master/src/librustc/middle/liveness.rs#L1026
https://github.com/mozilla/rust/blob/master/src/librustc/middle/liveness.rs#L1374
https://github.com/mozilla/rust/blob/master/src/librustc/middle/resolve.rs#L961
https://github.com/mozilla/rust/blob/master/src/librustc/middle/resolve.rs#L1951
https://github.com/mozilla/rust/blob/master/src/librustc/middle/resolve.rs#L2398
https://github.com/mozilla/rust/blob/master/src/librustc/front/feature_gate.rs#L372
https://github.com/mozilla/rust/blob/master/src/librustc/metadata/filesearch.rs#L148
https://github.com/mozilla/rust/blob/master/src/librustc/metadata/creader.rs#L320
https://github.com/mozilla/rust/blob/master/src/librustc/metadata/creader.rs#L420
https://github.com/mozilla/rust/blob/master/src/librustc/metadata/loader.rs#L376

I guess it might not be useful to use cascade! in every code I quote though.

[dharmatech]

Candidates for method cascade usage in servo:

https://github.com/mozilla/servo/blob/master/src/components/gfx/render_context.rs#L56
https://github.com/mozilla/servo/blob/master/src/components/gfx/render_context.rs#L79
https://github.com/mozilla/servo/blob/master/src/components/gfx/render_context.rs#L256

[dharmatech]

draw_push_clip as it currently is:

https://gist.github.com/dharmatech/ded09b46ff700697aef6

How it would look with built-in support for method cascades:

https://gist.github.com/dharmatech/16000fa777356ee74cbc

[emberian]

It doesn't need to be built-in to use it. The macro can be defined anywhere.

On Mon, May 19, 2014 at 10:50 AM, dharmatech notifications@github.comwrote:

draw_push_clip as it currently is:

https://gist.github.com/dharmatech/ded09b46ff700697aef6

How it would look with built-in support for method cascades:

https://gist.github.com/dharmatech/16000fa777356ee74cbc

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[dharmatech]

rust-http - handle_request - after

q3 - render - after