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< ol class = "chapter" > < li class = "chapter-item expanded " > < a href = "introduction.html" > < strong aria-hidden = "true" > 1.< / strong > Introduction< / a > < / li > < li class = "chapter-item expanded " > < a href = "quickstart.html" class = "active" > < strong aria-hidden = "true" > 2.< / strong > Quickstart< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/index.html" > < strong aria-hidden = "true" > 3.< / strong > Type system< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "types/objects/index.html" > < strong aria-hidden = "true" > 3.1.< / strong > Objects< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "types/objects/complex_fields.html" > < strong aria-hidden = "true" > 3.1.1.< / strong > Complex fields< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/objects/context.html" > < strong aria-hidden = "true" > 3.1.2.< / strong > Context< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/objects/error/index.html" > < strong aria-hidden = "true" > 3.1.3.< / strong > Error handling< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "types/objects/error/field.html" > < strong aria-hidden = "true" > 3.1.3.1.< / strong > Field errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/objects/error/schema.html" > < strong aria-hidden = "true" > 3.1.3.2.< / strong > Schema errors< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "types/objects/generics.html" > < strong aria-hidden = "true" > 3.1.4.< / strong > Generics< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "types/interfaces.html" > < strong aria-hidden = "true" > 3.2.< / strong > Interfaces< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/unions.html" > < strong aria-hidden = "true" > 3.3.< / strong > Unions< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/enums.html" > < strong aria-hidden = "true" > 3.4.< / strong > Enums< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/input_objects.html" > < strong aria-hidden = "true" > 3.5.< / strong > Input objects< / a > < / li > < li class = "chapter-item expanded " > < a href = "types/scalars.html" > < strong aria-hidden = "true" > 3.6.< / strong > Scalars< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "schema/index.html" > < strong aria-hidden = "true" > 4.< / strong > Schema< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "schema/subscriptions.html" > < strong aria-hidden = "true" > 4.1.< / strong > Subscriptions< / a > < / li > < li class = "chapter-item expanded " > < a href = "schema/introspection.html" > < strong aria-hidden = "true" > 4.2.< / strong > Introspection< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "serve/index.html" > < strong aria-hidden = "true" > 5.< / strong > Serving< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "serve/batching.html" > < strong aria-hidden = "true" > 5.1.< / strong > Batching< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "advanced/index.html" > < strong aria-hidden = "true" > 6.< / strong > Advanced Topics< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "advanced/implicit_and_explicit_null.html" > < strong aria-hidden = "true" > 6.1.< / strong > Implicit and explicit null< / a > < / li > < li class = "chapter-item expanded " > < a href = "advanced/n_plus_1.html" > < strong aria-hidden = "true" > 6.2.< / strong > N+1 problem< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "advanced/dataloader.html" > < strong aria-hidden = "true" > 6.2.1.< / strong > DataLoader< / a > < / li > < li class = "chapter-item expanded " > < a href = "advanced/lookahead.html" > < strong aria-hidden = "true" > 6.2.2.< / strong > Look-ahead< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "advanced/eager_loading.html" > < strong aria-hidden = "true" > 6.2.2.1.< / strong > Eager loading< / a > < / li > < / ol > < / li > < / ol > < / li > < / ol > < / li > < / ol >
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< h1 id = "quickstart" > < a class = "header" href = "#quickstart" > Quickstart< / a > < / h1 >
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< p > This page will give you a short introduction to the concepts in < a href = "https://docs.rs/juniper" > Juniper< / a > .< / p >
< p > < strong > < a href = "https://docs.rs/juniper" > Juniper< / a > follows a < a href = "https://www.apollographql.com/blog/backend/architecture/schema-first-vs-code-only-graphql#code-only" > code-first< / a > approach to define a < a href = "https://graphql.org" > GraphQL< / a > schema.< / strong > < / p >
< blockquote >
< p > < strong > TIP< / strong > : For a < a href = "https://www.apollographql.com/blog/backend/architecture/schema-first-vs-code-only-graphql#schema-first" > schema-first< / a > approach, consider using a < a href = "https://docs.rs/juniper-from-schema" > < code > juniper-from-schema< / code > < / a > crate for generating a < a href = "https://docs.rs/juniper" > < code > juniper< / code > < / a > -based code from a < a href = "https://graphql.org/learn/schema" > schema< / a > file.< / p >
< / blockquote >
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< h2 id = "installation" > < a class = "header" href = "#installation" > Installation< / a > < / h2 >
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< pre > < code class = "language-toml" > [dependencies]
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juniper = "0.16.0"
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< / code > < / pre >
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< h2 id = "schema" > < a class = "header" href = "#schema" > Schema< / a > < / h2 >
< p > Exposing simple enums and structs as < a href = "https://graphql.org" > GraphQL< / a > types is just a matter of adding a custom < a href = "https://doc.rust-lang.org/stable/reference/attributes/derive.html#derive" > derive attribute< / a > to them. < a href = "https://docs.rs/juniper" > Juniper< / a > includes support for basic < a href = "https://www.rust-lang.org" > Rust< / a > types that naturally map to < a href = "https://graphql.org" > GraphQL< / a > features, such as < code > Option< T> < / code > , < code > Vec< T> < / code > , < code > Box< T> < / code > , < code > Arc< T> < / code > , < code > String< / code > , < code > f64< / code > , < code > i32< / code > , references, slices and arrays.< / p >
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< p > For more advanced mappings, < a href = "https://docs.rs/juniper" > Juniper< / a > provides multiple macros to map your < a href = "https://www.rust-lang.org" > Rust< / a > types to a < a href = "https://graphql.org/learn/schema" > GraphQL schema< / a > . The most important one is the < a href = "https://docs.rs/juniper/0.16.0/juniper/macro.graphql_object.html" > < code > #[graphql_object]< / code > attribute< / a > that is used for declaring a < a href = "https://spec.graphql.org/October2021#sec-Objects" > GraphQL object< / a > with resolvers (typically used for declaring < a href = "https://spec.graphql.org/October2021#sec-Root-Operation-Types" > < code > Query< / code > and < code > Mutation< / code > roots< / a > ).< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > # ![allow(unused_variables)]
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< / span > < span class = "boring" > extern crate juniper;
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< / span > < span class = "boring" >
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< / span > < span class = "boring" > use std::fmt::Display;
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< / span > < span class = "boring" >
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< / span > use juniper::{
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graphql_object, EmptySubscription, FieldResult, GraphQLEnum,
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GraphQLInputObject, GraphQLObject, ScalarValue,
};
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< span class = "boring" >
< / span > < span class = "boring" > struct DatabasePool;
< / span > < span class = "boring" > impl DatabasePool {
< / span > < span class = "boring" > fn get_connection(& self) -> FieldResult< DatabasePool> { Ok(DatabasePool) }
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< / span > < span class = "boring" > fn find_human(& self, _id: & str) -> FieldResult< Human> { Err("")? }
< / span > < span class = "boring" > fn insert_human(& self, _human: & NewHuman) -> FieldResult< Human> { Err("")? }
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< / span > < span class = "boring" > }
< / span >
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#[derive(GraphQLEnum)]
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enum Episode {
NewHope,
Empire,
Jedi,
}
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#[derive(GraphQLObject)]
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#[graphql(description = "A humanoid creature in the Star Wars universe")]
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struct Human {
id: String,
name: String,
appears_in: Vec< Episode> ,
home_planet: String,
}
// There is also a custom derive for mapping GraphQL input objects.
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#[derive(GraphQLInputObject)]
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#[graphql(description = "A humanoid creature in the Star Wars universe")]
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struct NewHuman {
name: String,
appears_in: Vec< Episode> ,
home_planet: String,
}
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// Now, we create our root `Query` and `Mutation` types with resolvers by using
// the `#[graphql_object]` attribute.
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// Resolvers can have a context that allows accessing shared state like a
// database pool.
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struct Context {
// Use your real database pool here.
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db: DatabasePool,
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}
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// To make our `Context` usable by `juniper`, we have to implement a marker
// trait.
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impl juniper::Context for Context {}
struct Query;
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// Here we specify the context type for the object.
// We need to do this in every type that needs access to the `Context`.
#[graphql_object]
#[graphql(context = Context)]
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impl Query {
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// Note, that the field name will be automatically converted to the
// `camelCased` variant, just as GraphQL conventions imply.
fn api_version() -> & 'static str {
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"1.0"
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}
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fn human(
// Arguments to resolvers can either be simple scalar types, enums or
// input objects.
id: String,
// To gain access to the `Context`, we specify a `context`-named
// argument referring the correspondent `Context` type, and `juniper`
// will inject it automatically.
context: & Context,
) -> FieldResult< Human> {
// Get a `db` connection.
let conn = context.db.get_connection()?;
// Execute a `db` query.
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// Note the use of `?` to propagate errors.
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let human = conn.find_human(& id)?;
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// Return the result.
Ok(human)
}
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}
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// Now, we do the same for our `Mutation` type.
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struct Mutation;
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#[graphql_object]
#[graphql(
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context = Context,
// If we need to use `ScalarValue` parametrization explicitly somewhere
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// in the object definition (like here in `FieldResult`), we could
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// declare an explicit type parameter for that, and specify it.
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scalar = S: ScalarValue + Display,
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)]
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impl Mutation {
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fn create_human< S: ScalarValue + Display> (
new_human: NewHuman,
context: & Context,
) -> FieldResult< Human, S> {
let db = context.db.get_connection().map_err(|e| e.map_scalar_value())?;
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let human: Human = db.insert_human(& new_human).map_err(|e| e.map_scalar_value())?;
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Ok(human)
}
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}
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// Root schema consists of a query, a mutation, and a subscription.
// Request queries can be executed against a `RootNode`.
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type Schema = juniper::RootNode< 'static, Query, Mutation, EmptySubscription< Context> > ;
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {
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< / span > < span class = "boring" > _ = Schema::new(Query, Mutation, EmptySubscription::new());
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< / span > < span class = "boring" > }< / span > < / code > < / pre > < / pre >
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< p > Now we have a very simple but functional schema for a < a href = "https://graphql.org" > GraphQL< / a > server!< / p >
< p > To actually serve the < a href = "https://graphql.org/learn/schema" > schema< / a > , see the guides for our various < a href = "serve/index.html" > server integrations< / a > .< / p >
< h2 id = "execution" > < a class = "header" href = "#execution" > Execution< / a > < / h2 >
< p > < a href = "https://docs.rs/juniper" > Juniper< / a > is a library that can be used in many contexts: it doesn't require a server, nor it has a dependency on a particular transport or serialization format. You can invoke the < code > juniper::execute()< / code > directly to get a result for a < a href = "https://graphql.org" > GraphQL< / a > query:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > // Only needed due to 2018 edition because the macro is not accessible.
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< / span > < span class = "boring" > #[macro_use] extern crate juniper;
< / span > use juniper::{
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graphql_object, graphql_value, EmptyMutation, EmptySubscription,
GraphQLEnum, Variables,
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};
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#[derive(GraphQLEnum, Clone, Copy)]
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enum Episode {
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// Note, that the enum value will be automatically converted to the
// `SCREAMING_SNAKE_CASE` variant, just as GraphQL conventions imply.
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NewHope,
Empire,
Jedi,
}
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// Arbitrary context data.
struct Ctx(Episode);
impl juniper::Context for Ctx {}
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struct Query;
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#[graphql_object]
#[graphql(context = Ctx)]
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impl Query {
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fn favorite_episode(context: & Ctx) -> Episode {
context.0
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}
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}
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type Schema = juniper::RootNode< 'static, Query, EmptyMutation< Ctx> , EmptySubscription< Ctx> > ;
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fn main() {
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// Create a context.
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let ctx = Ctx(Episode::NewHope);
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// Run the execution.
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let (res, _errors) = juniper::execute_sync(
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"query { favoriteEpisode }",
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None,
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& Schema::new(Query, EmptyMutation::new(), EmptySubscription::new()),
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& Variables::new(),
& ctx,
).unwrap();
assert_eq!(
res,
graphql_value!({
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"favoriteEpisode": "NEW_HOPE",
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}),
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);
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}< / code > < / pre > < / pre >
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< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
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< a rel = "prev" href = "introduction.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
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< i class = "fa fa-angle-left" > < / i >
< / a >
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< a rel = "next prefetch" href = "types/index.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
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< i class = "fa fa-angle-right" > < / i >
< / a >
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< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
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< a rel = "prev" href = "introduction.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
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< i class = "fa fa-angle-left" > < / i >
< / a >
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< a rel = "next prefetch" href = "types/index.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
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< i class = "fa fa-angle-right" > < / i >
< / a >
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< / nav >
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< / div >
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< script >
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window.playground_copyable = true;
< / script >
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< script src = "elasticlunr.min.js" > < / script >
< script src = "mark.min.js" > < / script >
< script src = "searcher.js" > < / script >
< script src = "clipboard.min.js" > < / script >
< script src = "highlight.js" > < / script >
< script src = "book.js" > < / script >
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<!-- Custom JS scripts -->
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< / div >
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< / body >
< / html >
