练习：构建器类型

在此示例中，我们将实现一个拥有全部数据所有权的复杂数据类型。我们将使用 “构建器模式”来支持逐步构建新值，通过便捷函数来实现。

填补缺失的内容。

1. #[derive(Debug)]
2. enum Language {
3. Rust,
4. Java,
5. Perl,
6. }

8. #[derive(Clone, Debug)]
9. struct Dependency {
10. name: String,
11. version_expression: String,
12. }

14. /// A representation of a software package.
15. #[derive(Debug)]
16. struct Package {
17. name: String,
18. version: String,
19. authors: Vec<String>,
20. dependencies: Vec<Dependency>,
21. language: Option<Language>,
22. }

24. impl Package {
25. /// Return a representation of this package as a dependency, for use in
26. /// building other packages.
27. fn as_dependency(&self) -> Dependency {
28. todo!("1")
29. }
30. }

32. /// A builder for a Package. Use `build()` to create the `Package` itself.
33. struct PackageBuilder(Package);

35. impl PackageBuilder {
36. fn new(name: impl Into<String>) -> Self {
37. todo!("2")
38. }

40. /// Set the package version.
41. fn version(mut self, version: impl Into<String>) -> Self {
42. self.0.version = version.into();
43. self
44. }

46. /// Set the package authors.
47. fn authors(mut self, authors: Vec<String>) -> Self {
48. todo!("3")
49. }

51. /// Add an additional dependency.
52. fn dependency(mut self, dependency: Dependency) -> Self {
53. todo!("4")
54. }

56. /// Set the language. If not set, language defaults to None.
57. fn language(mut self, language: Language) -> Self {
58. todo!("5")
59. }

61. fn build(self) -> Package {
62. self.0
63. }
64. }

66. fn main() {
67. let base64 = PackageBuilder::new("base64").version("0.13").build();
68. println!("base64: {base64:?}");
69. let log =
70. PackageBuilder::new("log").version("0.4").language(Language::Rust).build();
71. println!("log: {log:?}");
72. let serde = PackageBuilder::new("serde")
73. .authors(vec!["djmitche".into()])
74. .version(String::from("4.0"))
75. .dependency(base64.as_dependency())
76. .dependency(log.as_dependency())
77. .build();
78. println!("serde: {serde:?}");
79. }