Playing with macros. Generated Attributes struct, attributes names vector and Default trait impl with a macro_rules

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>
2020-04-10 19:05:17 +02:00 · 2020-04-10 19:05:17 +02:00 · 27238b3f2f
parent e49453f4a6
commit 27238b3f2f
5 changed files with 117 additions and 62 deletions
--- a/README.md
+++ b/README.md
@ -6,11 +6,11 @@ Work in progress SDK for [CloudEvents](https://github.com/cloudevents/spec)

 |                               |  [v0.3](https://github.com/cloudevents/spec/tree/v0.3) | [v1.0](https://github.com/cloudevents/spec/tree/v1.0) |
 | :---------------------------: | :----------------------------------------------------------------------------: | :---------------------------------------------------------------------------------: |
-| CloudEvents Core              | :x: | :heavy_check_mark: |
+| CloudEvents Core              | :heavy_check_mark: | :heavy_check_mark: |
 | AMQP Protocol Binding         | :x: | :x:  |
 | AVRO Event Format             | :x: | :x: |
 | HTTP Protocol Binding         | :x: | :x: |
-| JSON Event Format             | :x: | :heavy_check_mark: |
+| JSON Event Format             | :heavy_check_mark: | :heavy_check_mark: |
 | Kafka Protocol Binding        | :x: | :x: |
 | MQTT Protocol Binding         | :x: | :x: |
 | NATS Protocol Binding         | :x: | :x: |
--- a/src/event/attributes.rs
+++ b/src/event/attributes.rs
@ -1,6 +1,79 @@
 use super::{AttributesV03, AttributesV10, SpecVersion};
 use chrono::{DateTime, Utc};

+macro_rules! attributes_def {
+    // struct attributes expansion
+    (@struct_gen $struct_name:ident {$(,)*} -> { $($out:tt)* }) => {
+        #[derive(PartialEq, Debug, Clone)]
+        pub struct $struct_name {
+            $($out)*
+        }
+    };
+    (@struct_gen $struct_name:ident {$element_name:ident $(as $_element_lit:literal)?: $element_ty:ty $({$($opts:tt)*})?, $($tail:tt)*} -> {}) => {
+        attributes_def!(@struct_gen $struct_name { $($tail)* } -> {pub(crate) $element_name: $element_ty});
+    };
+    (@struct_gen $struct_name:ident {$element_name:ident $(as $_element_lit:literal)?: $element_ty:ty $({$($opts:tt)*})?, $($tail:tt)*} -> {$($out:tt)*}) => {
+        attributes_def!(@struct_gen $struct_name { $($tail)* } -> {$($out)*, pub(crate) $element_name: $element_ty});
+    };
+
+    // count attributes
+    (@count_attrs ) => {0usize};
+    (@count_attrs $_element_name:ident $(as $_element_lit:literal)?: $element_ty:ty $({$($opts:tt)*})?, $($tail:tt)*) => {1usize + attributes_def!{@count_attrs $($tail)* }};
+
+    // names expansion
+    (@attributes_gen {} -> {$($out:expr)*} ) => {
+        [$($out),*]
+    };
+    (@attributes_gen { $element_name:ident: $_element_ty:ty $({$($_opts:tt)*})?, $($tail:tt)* } -> {$($out:tt)*}) => {
+        attributes_def!(@attributes_gen {$($tail)*} -> {$($out)* stringify!($element_name)})
+    };
+    (@attributes_gen { $_element_name:ident as $element_lit:literal: $_element_ty:ty $({$($_opts:tt)*})? , $($tail:tt)* } -> {$($out:tt)*}) => {
+        attributes_def!(@attributes_gen {$($tail)*} -> {$($out)* $element_lit})
+    };
+
+    // attribute names expansion
+    (@attribute_names_gen $attr_vec_name:ident { $($attrs:tt)* }) => {
+        pub const $attr_vec_name: [&'static str; attributes_def!(@count_attrs $($attrs)*)] = attributes_def!(@attributes_gen { $($attrs)* } -> {});
+    };
+
+    // default trait implementation expansion
+    (@default_gen $struct_name:ident {$(,)*} -> { $($out:tt)* }) => {
+        impl Default for $struct_name {
+            fn default() -> Self {
+                $struct_name {
+                    $($out)*
+                }
+            }
+        }
+    };
+    (@default_gen $struct_name:ident {
+        $element_name:ident $(as $_element_lit:literal)?: $_element_ty:ty, $($tail:tt)*
+    } -> { $($out:tt)* } ) => {
+        attributes_def!(@default_gen $struct_name { $($tail)* } -> {$($out)* $element_name: attributes_def!(@default_gen_walk_opts {}), });
+    };
+    (@default_gen $struct_name:ident {
+        $element_name:ident $(as $_element_lit:literal)?: $_element_ty:ty {$($opts:tt)*}, $($tail:tt)*
+    } -> { $($out:tt)* } ) => {
+        attributes_def!(@default_gen $struct_name { $($tail)* } -> {$($out)* $element_name: attributes_def!(@default_gen_walk_opts {$($opts)*}), });
+    };
+    (@default_gen_walk_opts {default: $default_expr:expr, $($tail:tt)*}) => {
+        $default_expr
+    };
+    (@default_gen_walk_opts {$_opt_key:ident: $_opt_val:ident, $($tail:tt)*}) => {
+        attributes_def!(@default_gen_walk_opts {$($tail)*})
+    };
+    (@default_gen_walk_opts {}) => {
+        Default::default()
+    };
+
+    // Real macro input
+    ($struct_name:ident, $attr_names:ident, { $($tt:tt)* }) => {
+        attributes_def!(@attribute_names_gen $attr_names { $($tt)* });
+        attributes_def!(@struct_gen $struct_name { $($tt)* } -> {});
+        attributes_def!(@default_gen $struct_name { $($tt)* } -> {});
+    };
+}
+
 /// Trait to get [CloudEvents Context attributes](https://github.com/cloudevents/spec/blob/master/spec.md#context-attributes).
 pub trait AttributesReader {
    /// Get the [id](https://github.com/cloudevents/spec/blob/master/spec.md#id).
--- a/src/event/mod.rs
+++ b/src/event/mod.rs
@ -1,3 +1,4 @@
+#[macro_use]
 mod attributes;
 mod builder;
 mod data;
--- a/src/event/v03/attributes.rs
+++ b/src/event/v03/attributes.rs
@ -5,16 +5,25 @@ use chrono::{DateTime, Utc};
 use hostname::get_hostname;
 use uuid::Uuid;

-#[derive(PartialEq, Debug, Clone)]
-pub struct Attributes {
-    pub(crate) id: String,
-    pub(crate) ty: String,
-    pub(crate) source: String,
-    pub(crate) datacontenttype: Option<String>,
-    pub(crate) schemaurl: Option<String>,
-    pub(crate) subject: Option<String>,
-    pub(crate) time: Option<DateTime<Utc>>,
-}
+attributes_def!(
+    Attributes,
+    ATTRIBUTES_NAMES,
+    {
+        id: String {
+            default: Uuid::new_v4().to_string(),
+        },
+        ty as "type": String {
+            default: "rust.generated".to_string(),
+        },
+        source: String {
+            default: get_hostname().unwrap_or("http://localhost/".to_string()),
+        },
+        datacontenttype: Option<String>,
+        schemaurl: Option<String>,
+        subject: Option<String>,
+        time: Option<DateTime<Utc>>,
+    }
+);

 impl AttributesReader for Attributes {
    fn get_id(&self) -> &str {
@ -91,20 +100,6 @@ impl DataAttributesWriter for Attributes {
    }
 }

-impl Default for Attributes {
-    fn default() -> Self {
-        Attributes {
-            id: Uuid::new_v4().to_string(),
-            ty: "type".to_string(),
-            source: get_hostname().unwrap_or("http://localhost/".to_string()),
-            datacontenttype: None,
-            schemaurl: None,
-            subject: None,
-            time: None,
-        }
-    }
-}
-
 impl AttributesConverter for Attributes {
    fn into_v03(self) -> Self {
        self
--- a/src/event/v10/attributes.rs
+++ b/src/event/v10/attributes.rs
@ -4,16 +4,25 @@ use chrono::{DateTime, Utc};
 use hostname::get_hostname;
 use uuid::Uuid;

-#[derive(PartialEq, Debug, Clone)]
-pub struct Attributes {
-    pub(crate) id: String,
-    pub(crate) ty: String,
-    pub(crate) source: String,
-    pub(crate) datacontenttype: Option<String>,
-    pub(crate) dataschema: Option<String>,
-    pub(crate) subject: Option<String>,
-    pub(crate) time: Option<DateTime<Utc>>,
-}
+attributes_def!(
+    Attributes,
+    ATTRIBUTES_NAMES,
+    {
+        id: String {
+            default: Uuid::new_v4().to_string(),
+        },
+        ty as "type": String {
+            default: "rust.generated".to_string(),
+        },
+        source: String {
+            default: get_hostname().unwrap_or("http://localhost/".to_string()),
+        },
+        datacontenttype: Option<String>,
+        dataschema: Option<String>,
+        subject: Option<String>,
+        time: Option<DateTime<Utc>>,
+    }
+);

 impl AttributesReader for Attributes {
    fn get_id(&self) -> &str {
@ -33,24 +42,15 @@ impl AttributesReader for Attributes {
    }

    fn get_datacontenttype(&self) -> Option<&str> {
-        match self.datacontenttype.as_ref() {
-            Some(s) => Some(&s),
-            None => None,
-        }
+        self.datacontenttype.as_deref()
    }

    fn get_dataschema(&self) -> Option<&str> {
-        match self.dataschema.as_ref() {
-            Some(s) => Some(&s),
-            None => None,
-        }
+        self.dataschema.as_deref()
    }

    fn get_subject(&self) -> Option<&str> {
-        match self.subject.as_ref() {
-            Some(s) => Some(&s),
-            None => None,
-        }
+        self.subject.as_deref()
    }

    fn get_time(&self) -> Option<&DateTime<Utc>> {
@ -90,20 +90,6 @@ impl DataAttributesWriter for Attributes {
    }
 }

-impl Default for Attributes {
-    fn default() -> Self {
-        Attributes {
-            id: Uuid::new_v4().to_string(),
-            ty: "type".to_string(),
-            source: get_hostname().unwrap_or("http://localhost/".to_string()),
-            datacontenttype: None,
-            dataschema: None,
-            subject: None,
-            time: None,
-        }
-    }
-}
-
 impl AttributesConverter for Attributes {
    fn into_v10(self) -> Self {
        self