[−][src]Trait structural::field::multi_fields::RevGetMultiField

pub trait RevGetMultiField<'a, This: ?Sized + 'a>: RevGetMultiFieldImpl<'a, This> {
    type Fields: 'a;
    fn rev_get_multi_field(self, this: &'a This) -> Self::Fields;
}

Gets references to multiple fields from This, usually a tuple of Option<&_>s and &_s

This trait has a blanket implementation for the RevGetMultiFieldImpl trait, implementing that trait is necessary to be able to use this trait.

This is used by the StructuralExt::fields, and StructuralExt::cloned_fields methods.

There's also the RevGetMultiFieldOut type alias to get this trait's Fields associated type.

Example

This demonstrates how you can use RevGetMultiField with structs.

use structural::{StructuralExt, FP, fp};
use structural::field::RevGetMultiField;
use structural::for_examples::{Tuple2, Tuple3};

use std::cmp::Ordering;

fn access_fields<'a,T,O0,O1>(this: &'a T)->(&'a O0,&'a O1)
where
    // The `Fields= (&'a O0,&'a O1)` constraint ensures that the return type is a pair.
    FP!(0,1): RevGetMultiField<'a,T,Fields= (&'a O0,&'a O1)>
{
    this.fields(fp!(0,1))
}

let tup2 = Tuple2(Some(8), Ordering::Less);
let tup3 = Tuple3(Some("hello"), Some(true), 34);

assert_eq!( access_fields(&tup2), (&Some(8), &Ordering::Less) );
assert_eq!( access_fields(&tup3), (&Some("hello"), &Some(true)) );

Example

This demonstrates how you can use RevGetMultiField with enums.

use structural::{StructuralExt, FP};
use structural::path::IntoAliasingOut;
use structural::field::{RevGetMultiField,RevGetMultiFieldOut};
use structural::for_examples::{Bomb, WithBoom};

use std::cmp::Ordering;

// Used `IntoAliasingOut` here to make the path safely constructible,
// since cosntructing a `NestedFieldPathSet<_,_,UniquePaths>`
// (what `FP!(::Boom=>a,b)` desugars into) requires unsafe code to construct,
// while `NestedFieldPathSet<_,_,AliasedPaths>`
// (what `IntoAliasingOut` turns `FP!(::Boom=>a,b)` into)
// does not require unsafe code to construct
//
// While this is safely constructible,it can't be used to do multiple mutable borrows,
// you can use `field_path_aliases` to avoid writing `unsafe` code in that case.
type ThePath=IntoAliasingOut<FP!(::Boom=>a,b)>;

fn access_fields<'a,T,O0,O1>(this: &'a T)->Option<(&'a O0,&'a O1)>
where
    // The `Fields= Option<(&'a O0,&'a O1)>` constraint ensures that
    // the return type is an optional pair.
    ThePath: RevGetMultiField<'a,T,Fields= Option<(&'a O0,&'a O1)>>
{
    this.fields(ThePath::NEW)
}

fn main(){
    let with_0 = WithBoom::Nope;
    let with_1 = WithBoom::Boom{a:"hi", b: &[0,1,2]};
    assert_eq!( access_fields(&with_0), None );
    assert_eq!( access_fields(&with_1), Some((&"hi", &&[0,1,2][..])) );
    
    let bomb_0 = Bomb::Nope;
    let bomb_1 = Bomb::Boom{a:"hello", b: &[5,8,13]};
    assert_eq!( access_fields(&bomb_0), None );
    assert_eq!( access_fields(&bomb_1), Some((&"hello", &&[5,8,13][..])) );
}

Associated Types

type Fields: 'a

This is usually a tuple of Option<&_>s and &_s.

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Required methods

fn rev_get_multi_field(self, this: &'a This) -> Self::Fields

Gets references to multiple fields from this, usually a tuple of Option<&_>s and &_s.

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Implementors

impl<'a, This: ?Sized, Path> RevGetMultiField<'a, This> for Path where
    This: 'a,
    Path: RevGetMultiFieldImpl<'a, This>, [src]

type Fields = NormalizeFieldsOut<Path::UnnormFields>

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