属性保持完整，这意味着在访问时，它们表示为 syn::Attribute。然而，从标记中解析所有属性可能代价高昂且浪费，这就是为什么它们是懒加载的，并且只有在访问时才进行解析。

功能

默认情况下，所有功能都启用。

• derive 重新导出 aggregate_derive。

• impl 为常见类型如 Option<T> 添加默认实现。

• fmt 为 Amalgamate 实现 fmt::Debug。

用法

aggregate 的使用非常简单。

为了聚合结构体/枚举/联合的属性，只需进行 derive

// The prelude is not required for derive,
// however in order to use `aggregate`,
// the trait must be in scope
use aggregate::prelude::*;

/// This attribute is paired with the type
#[derive(Aggregate)]
struct Config {
  /// This attribute is paired with the field
  switch: bool,
}

Aggregate 支持嵌套

/// This attribute is paired with the type.
#[derive(Aggregate)]
struct ConfigFile {
  /// This attribute is paired with the field
  ///
  /// This field has an `inner`, which will 
  /// include the aggregation of `Config`
  ///
  /// In order for `aggregate_derive` to notice 
  /// nested structures, you must mark the field 
  /// with the `#[aggregate]` attribute:
  #[aggregate]
  my_config: Config,
}

在枚举变体中不需要 #[aggregate] 属性，但在枚举变体的结构体和元组内部需要再次添加

#[derive(Aggregate)]
enum MyEnum {
  /// Variants are automatically included
  VariantOne {
    /// Fields must be marked
    #[aggregate]
    field_1: Inner,
  },

  /// Unnamed structs like this are also 
  /// supported; `aggregate` simply enumerates 
  /// the fields for representation
  VariantTwo(#[aggregate] Inner),
}