Lib.rs

此包导出一个宏 Struct 用于实例化具有共同字段的 struct，用法类似于 struct update 语法，但允许不同类型，并且必须提供字段名称。

用法

let a = Struct! { StructA,
    field: value,
    ...
    [field2, field3, ...]: other,
    ...
};

展开为

let a = StructA {
   field: value,
   ...
   field2: other.field2,
   field3: other.field3,
   ...
};

示例

struct A {
    f1: i32,
    f2: &'static str,
    f3: i64,
    f4: &'static str,
    f5: u64,
}
struct B {
    f3: i64,
    f4: &'static str,
}
struct C {
    f5: u64,
}

let b = B { f3: 5, f4: "tt" };
let c = C { f5: 7 };

use struct_update::Struct;
let a = Struct! {A,
            f1: 3 + 5,
            f2: "sss",
            [f3, f4]: ..b,
            [f5]: ..c,
        };
assert_eq!(a.f1, 8);
assert_eq!(a.f2, "sss");
assert_eq!(a.f3, b.f3);
assert_eq!(a.f4, b.f4);
assert_eq!(a.f5, c.f5);

宏路径的解决方案

遗憾的是，在宏上下文中，我们无法使用路径(::)来实例化 struct，解决方案是将路径转换为标识符。

用法

The as _Struct 是可选的，_Struct 是默认名称。

let a = Struct! { a_crate::a_mod::StructA as _Struct,
    field: value,
    ...
    [field2, field3, ...]: other,
    ...
};

展开为

let a = {
    use a_crate::a_mod::StructA as _Struct;
    _Struct {
       field: value,
       ...
       field2: other.field2,
       field3: other.field3,
       ...
    }
};