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ActiveSupport's delegate as a Rust macro: https://play.rust-lang.org/?gist=0a84cf255d85f19cb0279e8054fb46e6&version=nightly&mode=debug
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#![allow(dead_code)] | |
/// Create method to access field of sub-resource | |
/// | |
/// Similar to ActiveSupport's [`delegate`]. | |
/// | |
/// [`delegate`]: http://api.rubyonrails.org/classes/Module.html#method-i-delegate | |
/// | |
/// # Limitations | |
/// | |
/// - You need to specify the return type | |
/// - No prefixing, because `concat_idents` is [useless] | |
/// | |
/// [useless]: https://github.com/rust-lang/rust/issues/29599 | |
macro_rules! delegate { | |
(var $field:ident -> ($ty:ty) to $subresource:ident) => { | |
fn $field(&self) -> $ty { | |
&self.$subresource.$field | |
} | |
}; | |
(func $function:ident : ($($p:ident : $pt:ty),*) -> () to $subresource:ident) => { | |
fn $function(&self, $($p: $pt),*) { | |
self.$subresource.$function($($p),*) | |
} | |
}; | |
(func $function:ident : ($($p:ident : $pt:ty),*) -> ($ty:ty) to $subresource:ident) => { | |
fn $function(&self, $($p: $pt),*) -> $ty { | |
&self.$subresource.$function($($p),*) | |
} | |
}; | |
(func $function:ident<$($l:lifetime),*> : ($($p:ident : $pt:ty),*) -> () to $subresource:ident) => { | |
fn $function<$($l),*>(&self, $($p: $pt),*) { | |
self.$subresource.$function($($p),*) | |
} | |
}; | |
(func $function:ident<$($l:lifetime),*> : ($($p:ident : $pt:ty),*) -> ($ty:ty) to $subresource:ident) => { | |
fn $function<$($l),*>(&self, $($p: $pt),*) -> $ty { | |
&self.$subresource.$function($($p),*) | |
} | |
}; | |
} | |
enum Availability { Available, NotAvailable } | |
struct Variant { | |
color: String, | |
availability: Availability, | |
} | |
struct SpecificProduct { | |
title: String, | |
variant: Variant, | |
} | |
impl Variant { | |
fn color_string(&self) -> &str { | |
return &self.color | |
} | |
fn color_string1(&self, val: &str) { | |
println!("{}", val) | |
} | |
fn color_string2(&self, val: &str) -> &str { | |
println!("{}", val); | |
return &self.color | |
} | |
fn color_string3<'a>(&self, val: &'a str) -> &'a str { | |
return val | |
} | |
} | |
impl SpecificProduct { | |
fn title(&self) -> &str { &self.title } | |
delegate!(var color -> (&String) to variant); | |
delegate!(var availability -> (&Availability) to variant); | |
delegate!(func color_string : () -> (&str) to variant); | |
delegate!(func color_string1 : (val : &str) -> () to variant); | |
delegate!(func color_string3<'a> : (val : &'a str) -> (&'a str) to variant); | |
} | |
#[test] | |
fn success() { | |
let prod = SpecificProduct { | |
title: "Thingy".into(), | |
variant: Variant { | |
color: "Blue".into(), | |
availability: Availability::NotAvailable, | |
}, | |
}; | |
let a: &str = "Blue".into(); | |
prod.color_string3(a); | |
assert_eq!(prod.color_string(), &"Blue".to_string()); | |
} |
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