Struct synstructure::Structure

pub struct Structure<'a> { /* fields omitted */ }

A wrapper around a syn::DeriveInput which provides utilities for creating custom derive trait implementations.

Methods

impl<'a> Structure<'a>

pub fn new(ast: &'a DeriveInput) -> Self

Create a new Structure with the variants and fields from the passed-in DeriveInput.

pub fn variants(&self) -> &[VariantInfo<'a>]

Returns a slice of the variants in this Structure.

pub fn variants_mut(&mut self) -> &mut [VariantInfo<'a>]

Returns a mut slice of the variants in this Structure.

pub fn ast(&self) -> &'a DeriveInput

Returns a reference to the underlying syn AST node which this Structure was created from.

pub fn omitted_variants(&self) -> bool

True if any variants were omitted due to a filter_variants call.

pub fn each<F, R>(&self, f: F) -> TokenStream where
    F: FnMut(&BindingInfo) -> R,
    R: ToTokens, 

Runs the passed-in function once for each bound field, passing in a BindingInfo. and generating match arms which evaluate the returned tokens.

This method will ignore variants or fields which are ignored through the filter and filter_variant methods.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B(i32, i32),
        C(u32),
    }
};
let s = Structure::new(&di);

assert_eq!(
    s.each(|bi| quote!(println!("{:?}", #bi))).to_string(),

    quote!{
        A::B(ref __binding_0, ref __binding_1,) => {
            { println!("{:?}", __binding_0) }
            { println!("{:?}", __binding_1) }
        }
        A::C(ref __binding_0,) => {
            { println!("{:?}", __binding_0) }
        }
    }.to_string()
);

pub fn fold<F, I, R>(&self, init: I, f: F) -> TokenStream where
    F: FnMut(TokenStream, &BindingInfo) -> R,
    I: ToTokens,
    R: ToTokens, 

Runs the passed-in function once for each bound field, passing in the result of the previous call, and a BindingInfo. generating match arms which evaluate to the resulting tokens.

This method will ignore variants or fields which are ignored through the filter and filter_variant methods.

If a variant has been ignored, it will return the init value.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B(i32, i32),
        C(u32),
    }
};
let s = Structure::new(&di);

assert_eq!(
    s.fold(quote!(0), |acc, bi| quote!(#acc + #bi)).to_string(),

    quote!{
        A::B(ref __binding_0, ref __binding_1,) => {
            0 + __binding_0 + __binding_1
        }
        A::C(ref __binding_0,) => {
            0 + __binding_0
        }
    }.to_string()
);

pub fn each_variant<F, R>(&self, f: F) -> TokenStream where
    F: FnMut(&VariantInfo) -> R,
    R: ToTokens, 

Runs the passed-in function once for each variant, passing in a VariantInfo. and generating match arms which evaluate the returned tokens.

This method will ignore variants and not bind fields which are ignored through the filter and filter_variant methods.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B(i32, i32),
        C(u32),
    }
};
let s = Structure::new(&di);

assert_eq!(
    s.each_variant(|v| {
        let name = &v.ast().ident;
        quote!(println!(stringify!(#name)))
    }).to_string(),

    quote!{
        A::B(ref __binding_0, ref __binding_1,) => {
            println!(stringify!(B))
        }
        A::C(ref __binding_0,) => {
            println!(stringify!(C))
        }
    }.to_string()
);

pub fn filter<F>(&mut self, f: F) -> &mut Self where
    F: FnMut(&BindingInfo) -> bool, 

Filter the bindings created by this Structure object. This has 2 effects:

• The bindings will no longer appear in match arms generated by methods on this Structure or its subobjects.

• Impl blocks created with the bound_impl or unsafe_bound_impl method only consider type parameters referenced in the types of non-filtered fields.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B{ a: i32, b: i32 },
        C{ a: u32 },
    }
};
let mut s = Structure::new(&di);

s.filter(|bi| {
    bi.ast().ident == Some(syn::Ident::new("a", proc_macro2::Span::call_site()))
});

assert_eq!(
    s.each(|bi| quote!(println!("{:?}", #bi))).to_string(),

    quote!{
        A::B{ a: ref __binding_0, .. } => {
            { println!("{:?}", __binding_0) }
        }
        A::C{ a: ref __binding_0, } => {
            { println!("{:?}", __binding_0) }
        }
    }.to_string()
);

pub fn add_bounds(&mut self, mode: AddBounds) -> &mut Self

Specify which bounds should be generated by impl-generating functions such as gen_impl, bound_impl, and unsafe_bound_impl.

The default behaviour is to generate both field and generic bounds from type parameters.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

// Limit bounds to only generics.
s.add_bounds(AddBounds::Generics);

assert_eq!(
    s.bound_impl(quote!(krate::Trait), quote!{
        fn a() {}
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        #[doc(hidden)]
        const _DERIVE_krate_Trait_FOR_A: () = {
            extern crate krate;
            impl<T, U> krate::Trait for A<T, U>
                where T: krate::Trait,
                      U: krate::Trait
            {
                fn a() {}
            }
        };
    }.to_string()
);

pub fn filter_variants<F>(&mut self, f: F) -> &mut Self where
    F: FnMut(&VariantInfo) -> bool, 

Filter the variants matched by this Structure object. This has 2 effects:

• Match arms destructuring these variants will no longer be generated by methods on this Structure

• Impl blocks created with the bound_impl or unsafe_bound_impl method only consider type parameters referenced in the types of fields in non-fitered variants.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B(i32, i32),
        C(u32),
    }
};

let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "B");

assert_eq!(
    s.each(|bi| quote!(println!("{:?}", #bi))).to_string(),

    quote!{
        A::C(ref __binding_0,) => {
            { println!("{:?}", __binding_0) }
        }
        _ => {}
    }.to_string()
);

pub fn remove_variant(&mut self, idx: usize) -> &mut Self

Remove the variant at the given index.

Panics

Panics if the index is out of range.

pub fn bind_with<F>(&mut self, f: F) -> &mut Self where
    F: FnMut(&BindingInfo) -> BindStyle, 

Updates the BindStyle for each of the passed-in fields by calling the passed-in function for each BindingInfo.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B(i32, i32),
        C(u32),
    }
};
let mut s = Structure::new(&di);

s.bind_with(|bi| BindStyle::RefMut);

assert_eq!(
    s.each(|bi| quote!(println!("{:?}", #bi))).to_string(),

    quote!{
        A::B(ref mut __binding_0, ref mut __binding_1,) => {
            { println!("{:?}", __binding_0) }
            { println!("{:?}", __binding_1) }
        }
        A::C(ref mut __binding_0,) => {
            { println!("{:?}", __binding_0) }
        }
    }.to_string()
);

pub fn binding_name<F>(&mut self, f: F) -> &mut Self where
    F: FnMut(&Field, usize) -> Ident, 

Updates the binding name for each fo the passed-in fields by calling the passed-in function for each BindingInfo.

The function will be called with the BindingInfo and its index in the enclosing variant.

The default name is __binding_{} where {} is replaced with an increasing number.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A {
        B{ a: i32, b: i32 },
        C{ a: u32 },
    }
};
let mut s = Structure::new(&di);

s.binding_name(|bi, i| bi.ident.clone().unwrap());

assert_eq!(
    s.each(|bi| quote!(println!("{:?}", #bi))).to_string(),

    quote!{
        A::B{ a: ref a, b: ref b, } => {
            { println!("{:?}", a) }
            { println!("{:?}", b) }
        }
        A::C{ a: ref a, } => {
            { println!("{:?}", a) }
        }
    }.to_string()
);

pub fn referenced_ty_params(&self) -> Vec<&'a Ident>

Returns a list of the type parameters which are refrenced in the types of non-filtered fields / variants.

Caveat

If the struct contains any macros in type position, all parameters will be considered bound. This is because we cannot determine which type parameters are bound by type macros.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T, i32),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "C");

assert_eq!(
    s.referenced_ty_params(),
    &[&(syn::Ident::new("T", proc_macro2::Span::call_site()))]
);

pub fn add_impl_generic(&mut self, param: GenericParam) -> &mut Self

Adds an impl<> generic parameter. This can be used when the trait to be derived needs some extra generic parameters.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);
let generic: syn::GenericParam = parse_quote!(X: krate::AnotherTrait);

assert_eq!(
    s.add_impl_generic(generic)
        .bound_impl(quote!(krate::Trait<X>),
        quote!{
                fn a() {}
        }
    ).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        #[doc(hidden)]
        const _DERIVE_krate_Trait_X_FOR_A: () = {
            extern crate krate;
            impl<T, U, X: krate::AnotherTrait> krate::Trait<X> for A<T, U>
                where T : krate :: Trait < X >,
                      Option<U>: krate::Trait<X>,
                      U: krate::Trait<X>
            {
                fn a() {}
            }
        };
    }.to_string()
);

pub fn add_trait_bounds(
    &self,
    bound: &TraitBound,
    where_clause: &mut Option<WhereClause>,
    mode: AddBounds
)

Add trait bounds for a trait with the given path for each type parmaeter referenced in the types of non-filtered fields.

Caveat

If the method contains any macros in type position, all parameters will be considered bound. This is because we cannot determine which type parameters are bound by type macros.

pub fn bound_impl<P: ToTokens, B: ToTokens>(
    &self,
    path: P,
    body: B
) -> TokenStream

NOTE: This methods' features are superceded by Structure::gen_impl.

Creates an impl block with the required generic type fields filled in to implement the trait path.

This method also adds where clauses to the impl requiring that all referenced type parmaeters implement the trait path.

Hygiene and Paths

This method wraps the impl block inside of a const (see the example below). In this scope, the first segment of the passed-in path is extern crate-ed in. If you don't want to generate that extern crate item, use a global path.

This means that if you are implementing my_crate::Trait, you simply write s.bound_impl(quote!(my_crate::Trait), quote!(...)), and for the entirety of the definition, you can refer to your crate as my_crate.

Caveat

If the method contains any macros in type position, all parameters will be considered bound. This is because we cannot determine which type parameters are bound by type macros.

Panics

Panics if the path string parameter is not a valid TraitBound.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "B");

assert_eq!(
    s.bound_impl(quote!(krate::Trait), quote!{
        fn a() {}
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        #[doc(hidden)]
        const _DERIVE_krate_Trait_FOR_A: () = {
            extern crate krate;
            impl<T, U> krate::Trait for A<T, U>
                where Option<U>: krate::Trait,
                      U: krate::Trait
            {
                fn a() {}
            }
        };
    }.to_string()
);

pub fn unsafe_bound_impl<P: ToTokens, B: ToTokens>(
    &self,
    path: P,
    body: B
) -> TokenStream

NOTE: This methods' features are superceded by Structure::gen_impl.

Creates an impl block with the required generic type fields filled in to implement the unsafe trait path.

This method also adds where clauses to the impl requiring that all referenced type parmaeters implement the trait path.

Hygiene and Paths

This method wraps the impl block inside of a const (see the example below). In this scope, the first segment of the passed-in path is extern crate-ed in. If you don't want to generate that extern crate item, use a global path.

This means that if you are implementing my_crate::Trait, you simply write s.bound_impl(quote!(my_crate::Trait), quote!(...)), and for the entirety of the definition, you can refer to your crate as my_crate.

Caveat

If the method contains any macros in type position, all parameters will be considered bound. This is because we cannot determine which type parameters are bound by type macros.

Panics

Panics if the path string parameter is not a valid TraitBound.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "B");

assert_eq!(
    s.unsafe_bound_impl(quote!(krate::Trait), quote!{
        fn a() {}
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        #[doc(hidden)]
        const _DERIVE_krate_Trait_FOR_A: () = {
            extern crate krate;
            unsafe impl<T, U> krate::Trait for A<T, U>
                where Option<U>: krate::Trait,
                      U: krate::Trait
            {
                fn a() {}
            }
        };
    }.to_string()
);

pub fn unbound_impl<P: ToTokens, B: ToTokens>(
    &self,
    path: P,
    body: B
) -> TokenStream

NOTE: This methods' features are superceded by Structure::gen_impl.

Creates an impl block with the required generic type fields filled in to implement the trait path.

This method will not add any where clauses to the impl.

Hygiene and Paths

This method wraps the impl block inside of a const (see the example below). In this scope, the first segment of the passed-in path is extern crate-ed in. If you don't want to generate that extern crate item, use a global path.

This means that if you are implementing my_crate::Trait, you simply write s.bound_impl(quote!(my_crate::Trait), quote!(...)), and for the entirety of the definition, you can refer to your crate as my_crate.

Panics

Panics if the path string parameter is not a valid TraitBound.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "B");

assert_eq!(
    s.unbound_impl(quote!(krate::Trait), quote!{
        fn a() {}
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        #[doc(hidden)]
        const _DERIVE_krate_Trait_FOR_A: () = {
            extern crate krate;
            impl<T, U> krate::Trait for A<T, U> {
                fn a() {}
            }
        };
    }.to_string()
);

pub fn unsafe_unbound_impl<P: ToTokens, B: ToTokens>(
    &self,
    path: P,
    body: B
) -> TokenStream

Deprecated

NOTE: This methods' features are superceded by Structure::gen_impl.

Creates an impl block with the required generic type fields filled in to implement the unsafe trait path.

This method will not add any where clauses to the impl.

Hygiene and Paths

This method wraps the impl block inside of a const (see the example below). In this scope, the first segment of the passed-in path is extern crate-ed in. If you don't want to generate that extern crate item, use a global path.

This means that if you are implementing my_crate::Trait, you simply write s.bound_impl(quote!(my_crate::Trait), quote!(...)), and for the entirety of the definition, you can refer to your crate as my_crate.

Panics

Panics if the path string parameter is not a valid TraitBound.

Example

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "B");

assert_eq!(
    s.unsafe_unbound_impl(quote!(krate::Trait), quote!{
        fn a() {}
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        #[doc(hidden)]
        const _DERIVE_krate_Trait_FOR_A: () = {
            extern crate krate;
            unsafe impl<T, U> krate::Trait for A<T, U> {
                fn a() {}
            }
        };
    }.to_string()
);

pub fn gen_impl(&self, cfg: TokenStream) -> TokenStream

Generate an impl block for the given struct. This impl block will automatically use hygiene tricks to avoid polluting the caller's namespace, and will automatically add trait bounds for generic type parameters.

Syntax

This function accepts its arguments as a TokenStream. The recommended way to call this function is passing the result of invoking the quote! macro to it.

s.gen_impl(quote! {
    // You can write any items which you want to import into scope here.
    // For example, you may want to include an `extern crate` for the
    // crate which implements your trait. These items will only be
    // visible to the code you generate, and won't be exposed to the
    // consuming crate
    extern crate krate;

    // You can also add `use` statements here to bring types or traits
    // into scope.
    //
    // WARNING: Try not to use common names here, because the stable
    // version of syn does not support hygiene and you could accidentally
    // shadow types from the caller crate.
    use krate::Trait as MyTrait;

    // The actual impl block is a `gen impl` or `gen unsafe impl` block.
    // You can use `@Self` to refer to the structure's type.
    gen impl MyTrait for @Self {
        fn f(&self) { ... }
    }
})

The most common usage of this trait involves loading the crate the target trait comes from with extern crate, and then invoking a gen impl block.

Hygiene

This method tries to handle hygiene intelligenly for both stable and unstable proc-macro implementations, however there are visible differences.

The output of every gen_impl function is wrapped in a dummy const value, to ensure that it is given its own scope, and any values brought into scope are not leaked to the calling crate. For example, the above invocation may generate an output like the following:

const _DERIVE_krate_Trait_FOR_Struct: () = {
    extern crate krate;
    use krate::Trait as MyTrait;
    impl<T> MyTrait for Struct<T> where T: MyTrait {
        fn f(&self) { ... }
    }
};

Using the std crate

If you are using quote!() to implement your trait, with the proc-macro2/nightly feature, std isn't considered to be in scope for your macro. This means that if you use types from std in your procedural macro, you'll want to explicitly load it with an extern crate std;.

Absolute paths

You should generally avoid using absolute paths in your generated code, as they will resolve very differently when using the stable and nightly versions of proc-macro2. Instead, load the crates you need to use explictly with extern crate and

Trait Bounds

This method will automatically add trait bounds for any type parameters which are referenced within the types of non-ignored fields.

Additional type parameters may be added with the generics syntax after the impl keyword.

Type Macro Caveat

If the method contains any macros in type position, all parameters will be considered bound. This is because we cannot determine which type parameters are bound by type macros.

Panics

This function will panic if the input TokenStream is not well-formed, or if additional type parameters added by impl<..> conflict with generic type parameters on the original struct.

Example Usage

let di: syn::DeriveInput = parse_quote! {
    enum A<T, U> {
        B(T),
        C(Option<U>),
    }
};
let mut s = Structure::new(&di);

s.filter_variants(|v| v.ast().ident != "B");

assert_eq!(
    s.gen_impl(quote! {
        extern crate krate;
        gen impl krate::Trait for @Self {
            fn a() {}
        }
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        const _DERIVE_krate_Trait_FOR_A: () = {
            extern crate krate;
            impl<T, U> krate::Trait for A<T, U>
            where
                Option<U>: krate::Trait,
                U: krate::Trait
            {
                fn a() {}
            }
        };
    }.to_string()
);

// NOTE: You can also add extra generics after the impl
assert_eq!(
    s.gen_impl(quote! {
        extern crate krate;
        gen impl<X: krate::OtherTrait> krate::Trait<X> for @Self
        where
            X: Send + Sync,
        {
            fn a() {}
        }
    }).to_string(),
    quote!{
        #[allow(non_upper_case_globals)]
        const _DERIVE_krate_Trait_X_FOR_A: () = {
            extern crate krate;
            impl<X: krate::OtherTrait, T, U> krate::Trait<X> for A<T, U>
            where
                X: Send + Sync,
                Option<U>: krate::Trait<X>,
                U: krate::Trait<X>
            {
                fn a() {}
            }
        };
    }.to_string()
);

Use add_bounds to change which bounds are generated.

Trait Implementations

impl<'a> PartialEq<Structure<'a>> for Structure<'a>

fn eq(&self, other: &Structure<'a>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Structure<'a>) -> bool

This method tests for !=.

impl<'a> Clone for Structure<'a>

fn clone(&self) -> Structure<'a>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Eq for Structure<'a>

impl<'a> Debug for Structure<'a>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<'a> Hash for Structure<'a>

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].