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< h1 class = "menu-title" > Juniper Book (GraphQL server for Rust)< / h1 >
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< h1 id = "scalars" > < a class = "header" href = "#scalars" > Scalars< / a > < / h1 >
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< p > Scalars are the primitive types at the leaves of a GraphQL query: numbers,
strings, and booleans. You can create custom scalars to other primitive values,
but this often requires coordination with the client library intended to consume
the API you're building.< / p >
< p > Since any value going over the wire is eventually transformed into JSON, you're
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also limited in the data types you can use.< / p >
< p > There are two ways to define custom scalars.< / p >
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< ul >
< li > For simple scalars that just wrap a primitive type, you can use the newtype pattern with
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a custom derive.< / li >
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< li > For more advanced use cases with custom validation, you can use
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the < code > graphql_scalar< / code > proc macro.< / li >
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< / ul >
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< h2 id = "built-in-scalars" > < a class = "header" href = "#built-in-scalars" > Built-in scalars< / a > < / h2 >
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< p > Juniper has built-in support for:< / p >
< ul >
< li > < code > i32< / code > as < code > Int< / code > < / li >
< li > < code > f64< / code > as < code > Float< / code > < / li >
< li > < code > String< / code > and < code > & str< / code > as < code > String< / code > < / li >
< li > < code > bool< / code > as < code > Boolean< / code > < / li >
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< li > < code > juniper::ID< / code > as < code > ID< / code > . This type is defined < a href = "https://spec.graphql.org/October2021#sec-ID" > in the
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spec< / a > as a type that is serialized
as a string but can be parsed from both a string and an integer.< / li >
< / ul >
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< p > Note that there is no built-in support for < code > i64< / code > /< code > u64< / code > , as the GraphQL spec < a href = "https://spec.graphql.org/October2021#sec-Int" > doesn't define any built-in scalars for < code > i64< / code > /< code > u64< / code > by default< / a > . You may wish to leverage a < a href = "#custom-scalars" > custom GraphQL scalar< / a > in your schema to support them.< / p >
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< p > < strong > Third party types< / strong > :< / p >
< p > Juniper has built-in support for a few additional types from common third party
crates. They are enabled via features that are on by default.< / p >
< ul >
< li > uuid::Uuid< / li >
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< li > chrono::{DateTime, NaiveDate, NaiveDateTime, NaiveTime}< / li >
< li > chrono_tz::Tz;< / li >
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< li > time::{Date, OffsetDateTime, PrimitiveDateTime, Time, UtcOffset}< / li >
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< li > url::Url< / li >
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< li > bson::oid::ObjectId< / li >
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< / ul >
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< h2 id = "custom-scalars" > < a class = "header" href = "#custom-scalars" > Custom scalars< / a > < / h2 >
< h3 id = "graphqltransparent-attribute" > < a class = "header" href = "#graphqltransparent-attribute" > < code > #[graphql(transparent)]< / code > attribute< / a > < / h3 >
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< p > Often, you might need a custom scalar that just wraps an existing type.< / p >
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< p > This can be done with the newtype pattern and a custom derive, similar to how
serde supports this pattern with < code > #[serde(transparent)]< / code > .< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" >
< / span > #[derive(juniper::GraphQLScalar)]
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#[graphql(transparent)]
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pub struct UserId(i32);
#[derive(juniper::GraphQLObject)]
struct User {
id: UserId,
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< p > < code > #[derive(GraphQLScalar)]< / code > is mostly interchangeable with < code > #[graphql_scalar]< / code >
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attribute:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" > use juniper::graphql_scalar;
< / span > < span class = "boring" >
< / span > #[graphql_scalar(transparent)]
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pub struct UserId {
value: i32,
}
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#[derive(juniper::GraphQLObject)]
struct User {
id: UserId,
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > That's it, you can now use < code > UserId< / code > in your schema.< / p >
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< p > The macro also allows for more customization:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > /// You can use a doc comment to specify a description.
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#[derive(juniper::GraphQLScalar)]
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#[graphql(
transparent,
// Overwrite the GraphQL type name.
name = " MyUserId" ,
// Specify a custom description.
// A description in the attribute will overwrite a doc comment.
description = " My user id description" ,
)]
pub struct UserId(i32);
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > All the methods used from newtype's field can be replaced with attributes:< / p >
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< h3 id = "graphqlto_output_with--fn-attribute" > < a class = "header" href = "#graphqlto_output_with--fn-attribute" > < code > #[graphql(to_output_with = < fn> )]< / code > attribute< / a > < / h3 >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > use juniper::{GraphQLScalar, ScalarValue, Value};
< / span > < span class = "boring" >
< / span > #[derive(GraphQLScalar)]
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#[graphql(to_output_with = to_output, transparent)]
struct Incremented(i32);
/// Increments [`Incremented`] before converting into a [`Value`].
fn to_output< S: ScalarValue> (v: & Incremented) -> Value< S> {
Value::from(v.0 + 1)
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h3 id = "graphqlfrom_input_with--fn-attribute" > < a class = "header" href = "#graphqlfrom_input_with--fn-attribute" > < code > #[graphql(from_input_with = < fn> )]< / code > attribute< / a > < / h3 >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > use juniper::{GraphQLScalar, InputValue, ScalarValue};
< / span > < span class = "boring" >
< / span > #[derive(GraphQLScalar)]
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#[graphql(from_input_with = Self::from_input, transparent)]
struct UserId(String);
impl UserId {
/// Checks whether [`InputValue`] is `String` beginning with `id: ` and
/// strips it.
fn from_input< S> (input: & InputValue< S> ) -> Result< Self, String>
where
S: ScalarValue
{
input.as_string_value()
.ok_or_else(|| format!(" Expected `String`, found: {}" , input))
.and_then(|str| {
str.strip_prefix(" id: " )
.ok_or_else(|| {
format!(
" Expected `UserId` to begin with `id: `, \
found: {}" ,
input,
)
})
})
.map(|id| Self(id.to_owned()))
}
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h3 id = "graphqlparse_token_with--fn-or-graphqlparse_tokentypes-attributes" > < a class = "header" href = "#graphqlparse_token_with--fn-or-graphqlparse_tokentypes-attributes" > < code > #[graphql(parse_token_with = < fn> ]< / code > or < code > #[graphql(parse_token(< types> )]< / code > attributes< / a > < / h3 >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > use juniper::{
< / span > < span class = "boring" > GraphQLScalar, InputValue, ParseScalarResult, ParseScalarValue,
< / span > < span class = "boring" > ScalarValue, ScalarToken, Value
< / span > < span class = "boring" > };
< / span > < span class = "boring" >
< / span > #[derive(GraphQLScalar)]
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#[graphql(
to_output_with = to_output,
from_input_with = from_input,
parse_token_with = parse_token,
// ^^^^^^^^^^^^^^^^ Can be replaced with `parse_token(String, i32)`
// which tries to parse as `String` and then as `i32`
// if prior fails.
)]
enum StringOrInt {
String(String),
Int(i32),
}
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fn to_output< S> (v: & StringOrInt) -> Value< S>
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where
S: ScalarValue
{
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match v {
StringOrInt::String(str) => Value::scalar(str.to_owned()),
StringOrInt::Int(i) => Value::scalar(*i),
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}
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}
fn from_input< S> (v: & InputValue< S> ) -> Result< StringOrInt, String>
where
S: ScalarValue
{
v.as_string_value()
.map(|s| StringOrInt::String(s.to_owned()))
.or_else(|| v.as_int_value().map(|i| StringOrInt::Int(i)))
.ok_or_else(|| format!(" Expected `String` or `Int`, found: {}" , v))
}
fn parse_token< S> (value: ScalarToken< '_> ) -> ParseScalarResult< '_, S>
where
S: ScalarValue
{
< String as ParseScalarValue< S> > ::from_str(value)
.or_else(|_| < i32 as ParseScalarValue< S> > ::from_str(value))
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< blockquote >
< p > < strong > NOTE:< / strong > As you can see, once you provide all 3 custom resolvers, there
is no need to follow < code > newtype< / code > pattern.< / p >
< / blockquote >
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< h3 id = "graphqlwith--path-attribute" > < a class = "header" href = "#graphqlwith--path-attribute" > < code > #[graphql(with = < path> )]< / code > attribute< / a > < / h3 >
< p > Instead of providing all custom resolvers, you can provide path to the < code > to_output< / code > ,
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< code > from_input< / code > , < code > parse_token< / code > functions.< / p >
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< p > Path can be simply < code > with = Self< / code > (default path where macro expects resolvers to be),
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in case there is an impl block with custom resolvers:< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > use juniper::{
< / span > < span class = "boring" > GraphQLScalar, InputValue, ParseScalarResult, ParseScalarValue,
< / span > < span class = "boring" > ScalarValue, ScalarToken, Value
< / span > < span class = "boring" > };
< / span > < span class = "boring" >
< / span > #[derive(GraphQLScalar)]
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// #[graphql(with = Self)] < - default behaviour
enum StringOrInt {
String(String),
Int(i32),
}
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impl StringOrInt {
fn to_output< S: ScalarValue> (& self) -> Value< S> {
match self {
Self::String(str) => Value::scalar(str.to_owned()),
Self::Int(i) => Value::scalar(*i),
}
}
fn from_input< S> (v: & InputValue< S> ) -> Result< Self, String>
where
S: ScalarValue,
{
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v.as_string_value()
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.map(|s| Self::String(s.to_owned()))
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.or_else(|| v.as_int_value().map(Self::Int))
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.ok_or_else(|| format!(" Expected `String` or `Int`, found: {}" , v))
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}
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fn parse_token< S> (value: ScalarToken< '_> ) -> ParseScalarResult< '_, S>
where
S: ScalarValue,
{
< String as ParseScalarValue< S> > ::from_str(value)
.or_else(|_| < i32 as ParseScalarValue< S> > ::from_str(value))
}
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > Or it can be path to a module, where custom resolvers are located.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > use juniper::{
< / span > < span class = "boring" > GraphQLScalar, InputValue, ParseScalarResult, ParseScalarValue,
< / span > < span class = "boring" > ScalarValue, ScalarToken, Value
< / span > < span class = "boring" > };
< / span > < span class = "boring" >
< / span > #[derive(GraphQLScalar)]
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#[graphql(with = string_or_int)]
enum StringOrInt {
String(String),
Int(i32),
}
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mod string_or_int {
use super::*;
pub(super) fn to_output< S> (v: & StringOrInt) -> Value< S>
where
S: ScalarValue,
{
match v {
StringOrInt::String(str) => Value::scalar(str.to_owned()),
StringOrInt::Int(i) => Value::scalar(*i),
}
}
pub(super) fn from_input< S> (v: & InputValue< S> ) -> Result< StringOrInt, String>
where
S: ScalarValue,
{
v.as_string_value()
.map(|s| StringOrInt::String(s.to_owned()))
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.or_else(|| v.as_int_value().map(StringOrInt::Int))
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.ok_or_else(|| format!(" Expected `String` or `Int`, found: {}" , v))
}
pub(super) fn parse_token< S> (value: ScalarToken< '_> ) -> ParseScalarResult< '_, S>
where
S: ScalarValue,
{
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< String as ParseScalarValue< S> > ::from_str(value)
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.or_else(|_| < i32 as ParseScalarValue< S> > ::from_str(value))
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}
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}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
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< p > Also, you can partially override < code > #[graphql(with)]< / code > attribute with other custom scalars.< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > use juniper::{GraphQLScalar, InputValue, ParseScalarResult, ScalarValue, ScalarToken, Value};
< / span > < span class = "boring" >
< / span > #[derive(GraphQLScalar)]
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#[graphql(parse_token(String, i32))]
enum StringOrInt {
String(String),
Int(i32),
}
impl StringOrInt {
fn to_output< S> (& self) -> Value< S>
where
S: ScalarValue,
{
match self {
Self::String(str) => Value::scalar(str.to_owned()),
Self::Int(i) => Value::scalar(*i),
}
}
fn from_input< S> (v: & InputValue< S> ) -> Result< Self, String>
where
S: ScalarValue,
{
v.as_string_value()
.map(|s| Self::String(s.to_owned()))
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.or_else(|| v.as_int_value().map(Self::Int))
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.ok_or_else(|| format!(" Expected `String` or `Int`, found: {}" , v))
}
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / code > < / pre > < / pre >
< h3 id = "using-foreign-types-as-scalars" > < a class = "header" href = "#using-foreign-types-as-scalars" > Using foreign types as scalars< / a > < / h3 >
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< p > For implementing custom scalars on foreign types there is < code > #[graphql_scalar]< / code > attribute macro.< / p >
< blockquote >
< p > < strong > NOTE:< / strong > To satisfy < a href = "https://doc.rust-lang.org/reference/items/implementations.html#orphan-rules" > orphan rules< / a > you should provide local < a href = "https://docs.rs/juniper/latest/juniper/trait.ScalarValue.html" > < code > ScalarValue< / code > < / a > implementation.< / p >
< / blockquote >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" > < span class = "boring" > extern crate juniper;
< / span > < span class = "boring" > mod date {
< / span > < span class = "boring" > pub struct Date;
< / span > < span class = "boring" > impl std::str::FromStr for Date {
< / span > < span class = "boring" > type Err = String;
< / span > < span class = "boring" >
< / span > < span class = "boring" > fn from_str(_value: & str) -> Result< Self, Self::Err> {
< / span > < span class = "boring" > unimplemented!()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > impl std::fmt::Display for Date {
< / span > < span class = "boring" > fn fmt(& self, _f: & mut std::fmt::Formatter) -> std::fmt::Result {
< / span > < span class = "boring" > unimplemented!()
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" > }
< / span > < span class = "boring" >
< / span > < span class = "boring" > use juniper::DefaultScalarValue as CustomScalarValue;
< / span > use juniper::{graphql_scalar, InputValue, ScalarValue, Value};
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#[graphql_scalar(
with = date_scalar,
parse_token(String),
scalar = CustomScalarValue,
// ^^^^^^^^^^^^^^^^^ Local `ScalarValue` implementation.
)]
type Date = date::Date;
// ^^^^^^^^^^ Type from another crate.
mod date_scalar {
use super::*;
pub(super) fn to_output(v: & Date) -> Value< CustomScalarValue> {
Value::scalar(v.to_string())
}
pub(super) fn from_input(v: & InputValue< CustomScalarValue> ) -> Result< Date, String> {
v.as_string_value()
.ok_or_else(|| format!(" Expected `String`, found: {}" , v))
.and_then(|s| s.parse().map_err(|e| format!(" Failed to parse `Date`: {}" , e)))
}
}
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< span class = "boring" >
< / span > < span class = "boring" > fn main() {}
< / span > < / 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 = "../types/input_objects.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" href = "../types/unions.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 >
< 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 = "../types/input_objects.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" href = "../types/unions.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 type = "text/javascript" >
window.playground_copyable = true;
< / script >
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< script src = "../elasticlunr.min.js" type = "text/javascript" charset = "utf-8" > < / script >
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