Type System Tricks for the Real World

Have you ever looked at some of the more exotic capabilities of Rust's type system and wondered “why”? Why on earth would I ever want a zero sized type? How do I efficiently implement a deeply recursive type? Just what do monomorphization and type erasure actually mean?

In this talk we'll look at some real world examples from inside Diesel to answer these questions and more. You'll come away from this talk with a stronger understanding of how to use Rust's generics, traits, and exotically sized types.

Transcript

1. Type System Tricks for the Real World
2. fn main() { break rust; // Can you read this color scheme? }
3. Who am I? • Sean Griffin • 10x Hacker Ninja Guru at Shopify • Rails Committer • Maintainer of Active Record • Creator of Diesel • Bikeshed co-host
6. Programming is full of trade-offs
7. Haskell • Pros • Expressive type system • Cons • No control over data layout
8. C • Pros • Tight control over data layout • Cons • "type" system
10. Rust's Fireflower
11. Rust's Fireflower
12. Rust's Fireflower
13. pub struct HashSet<K> { map: HashMap<K, ()> } impl<K: Hash + Eq> HashSet<K> { pub fn insert(&mut self, value: K) { self.map.insert(value, ()); } pub fn contains(&self, value: &K) -> bool { self.map.contains_key(value) } }
14. class Set def initialize @hash = {} end def insert(value) @hash[value] = true end def contains(value) @hash.key?(value) end end
15. char
16. struct Foo { bar: char, }
17. struct Foo { bar: char, baz: char, }
18. enum Foo { Bar(char), }
19. enum Foo { Bar(char), Baz, }
20. struct Baz;
21. enum Foo { Bar(char), Baz, }
22. enum Foo { Bar(char), Baz(u64), }
23. enum ListString { Cons { head: char, tail: ListString, }, Nil, }
24. enum ListString { Cons { head: char, tail: ListString, }, Nil, }
25. enum ListString { Cons { head: char, tail: ListString, }, Nil, }
26. enum ListString { Cons { head: char, tail: ListString, }, Nil, }
27. enum ListString { Cons { head: char, tail: ListString, }, Nil, }
28. error[E0072]: recursive type `ListString` has infinite size --> src/main.rs:1:1 | 1 | enum ListString { | ^^^^^^^^^^^^^^^ recursive type has infinite size ... 4 | tail: ListString, | ---------------- recursive without indirection | = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `ListString` representable
29. enum ListString { Cons { head: char, tail: ListString, }, Nil, }
30. enum ListString { Cons { head: char, tail: Box<ListString>, }, Nil, }
31. pub struct Cons<Tail> { head: char, tail: Tail, } pub struct Nil;
32. struct Pizza<Topping> { topping: Topping }
33. struct Pinapple; struct Pizza<Topping> { topping: Topping } size_of::<Pizza<Pinapple>>()
34. struct Pinapple; struct Pizza<Topping> { topping: Topping } size_of::<Pizza<Pinapple>>() // => Error: // Pineapple doesn't go on pizza, Steve. Fite me.
35. struct Pizza<Topping> { topping: Topping } size_of::<Pizza<u8>>()
36. pub struct Cons<Tail> { head: char, tail: Tail, } pub struct Nil;
37. Nil
38. Cons<Nil>
39. Cons<Cons<Nil>>
40. Cons<Cons<Cons<Nil>> >
41. pub struct Cons<Tail> { head: char, tail: Tail, } pub struct Nil;
42. This isn't without tradeoffs
43. fn do_stuff_with_string(s: ListString) { // doing stuff! }
44. fn do_stuff_with_string<T: ListString>(s: T) { // doing stuff! }
45. fn string_contains_a(s: ListString) -> bool { match s { Cons { head: 'a', .. } => true, Cons { tail, .. } => string_contains_a(tail), Nil => false, } }
46. fn string_contains_a<T: ListString>(s: T) -> bool { match s.unpack() { Some(('a', _)) => true, Some((_, tail)) => string_contains_a(tail), None => false, } }
48. trait Robot { fn username(&self) -> &str; } fn say_hi<T: Robot>(robot: &T) { println!("Hi, {}", robot.username()); }
49. struct Bors; impl Robot for Bors { fn username(&self) -> &str { "@bors" } }
50. struct Bors; impl Robot for Bors { fn username(&self) -> &str { "@bors" } } struct Alex; impl Robot for Alex { fn username(&self) -> &str { "@alexcrichton" } }
51. struct Bors; impl Robot for Bors { fn username(&self) -> &str { "@bors" } } struct Alex; impl Robot for Alex { fn username(&self) -> &str { "@alexcrichton" } }
52. struct Bors; fn Robot_username_Bors(_: &Bors) -> &str { "@bors" } struct Alex; impl Robot for Alex { fn username(&self) -> &str { "@alexcrichton" } }
53. struct Bors; fn Robot_username_Bors(_: &Bors) -> &str { "@bors" } struct Alex; impl Robot for Alex { fn username(&self) -> &str { "@alexcrichton" } }
54. struct Bors; fn Robot_username_Bors(_: &Bors) -> &str { "@bors" } struct Alex; fn Robot_username_Alex(_: &Alex) -> &str { "@alexcrichton" }
55. fn say_hi<T: Robot>(robot: &T) { println!("Hi, {}", robot.username()); }
56. fn say_hi_Bors(bors: &Bors) { println!("Hi, {}", Robot_username_Bors(bors)); } fn say_hi_Alex(alex: &Alex) { println!("Hi, {}", Robot_username_Alex(alex)); }
57. fn say_hi_Bors(bors: &Bors) { println!("Hi, {}", Robot_username_Bors(bors)); } fn say_hi_Alex(alex: &Alex) { println!("Hi, {}", Robot_username_Alex(alex)); }
58. fn say_hi_Bors(_: &Bors) { println!("Hi, {}", "@bors"); } fn say_hi_Alex(alex: &Alex) { println!("Hi, {}", Robot_username_Alex(alex)); }
59. fn say_hi_Bors(_: &Bors) { println!("Hi, {}", "@bors"); } fn say_hi_Alex(alex: &Alex) { println!("Hi, {}", Robot_username_Alex(alex)); }
60. fn say_hi_Bors(_: &Bors) { println!("Hi, {}", "@bors"); } fn say_hi_Alex(_: &Alex) { println!("Hi, {}", "@alexcrichton"); }
61. fn say_hi(robot: &Robot) { println!("Hi, {}", robot.username()); }
63. A real world example
64. #[test] fn complex_queries_with_no_data_have_no_size() { assert_eq!(0, mem::size_of_val(&users.as_query())); assert_eq!(0, mem::size_of_val(&users.select(id).as_query())); assert_eq!(0, mem::size_of_val( &users.inner_join(posts).filter(name.eq(title)) )); }
65. List of things you can do with a 0-size type •
66. users.find(1)
67. SelectStatement< users::table, DefaultSelectClause, NoDistinctClause, WhereClause< Eq< users::id, Bound<Integer, i32>, >, >, NoOrderClause, NoLimitClause, NoOffsetClause, NoGroupByClause, >
68. SelectStatement< users::table, DefaultSelectClause, NoDistinctClause, WhereClause< Eq< users::id, Bound<Integer, i32>, >, >, >
69. SelectStatement { select: DefaultSelectClause, from: users::table, distinct: NoDistinctClause, where_clause: WhereClause(Eq { left: users::id, right: Bound::new(1), }), }
70. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.distinct.walk_ast(out)?; self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
71. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.distinct.walk_ast(out)?; self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
72. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.distinct.walk_ast(out)?; self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
73. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); NoDistinctClause::walk_ast(out)?; self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
74. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); Ok(())?; self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
75. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
76. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
77. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); DefaultSelectClause::walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
78. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.from.default_selection() .walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
79. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.from.default_selection() .walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
80. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); (users::id, users::name) .walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
81. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); (users::id, users::name) .walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
82. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); if 0 != 0 { out.push_sql(", "); } users::id.walk_ast(out)?; if 1 != 0 { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?;
83. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); if 0 != 0 { out.push_sql(", "); } users::id.walk_ast(out)?; if 1 != 0 { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?;
84. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); if false { out.push_sql(", "); } users::id.walk_ast(out)?; if 1 != 0 { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?;
85. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); if false { out.push_sql(", "); } users::id.walk_ast(out)?; if 1 != 0 { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?;
86. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::id.walk_ast(out)?; if 1 != 0 { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
87. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::id.walk_ast(out)?; if 1 != 0 { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
88. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::id.walk_ast(out)?; if true { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
89. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::id.walk_ast(out)?; if true { out.push_sql(", "); } users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
90. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::id.walk_ast(out)?; out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
91. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::id.walk_ast(out)?; out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
92. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::table.walk_ast(out)?; out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
93. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); users::table.walk_ast(out)?; out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
94. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); out.push_identifier("users"); out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
95. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); out.push_sql("\""); out.push_sql(&"users".replace('"', "\"\"")); out.push_sql("\""); out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
96. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); out.push_sql("\""); out.push_sql(&"users".replace('"', "\"\"")); out.push_sql("\""); out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
97. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
98. out.push_sql("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_identifier("id"); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(())
99. out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql(&"id".replace('"', "\"\"")); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
100. out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql(&"id".replace('"', "\"\"")); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
101. out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
102. out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?;
103. out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
104. out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
105. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::name.walk_ast(out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
106. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::table.walk_ast(out)?; out.push_sql("."); out.push_identifier("name"); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
107. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); users::table.walk_ast(out)?; out.push_sql("."); out.push_identifier("name"); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
108. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_identifier("name"); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(())
109. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_identifier("name"); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(())
110. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); self.from.walk_ast(out)?;
111. out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); self.from.walk_ast(out)?;
112. out.push_sql(", "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(())
113. out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
114. out.push_sql("."); out.push_sql("\""); out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
115. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
116. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); self.where_clause.walk_ast(out)?; Ok(()) }
117. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); self.where_clause.walk_ast(out)?; Ok(()) }
118. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); self.where_clause.0.walk_ast(out)?; Ok(()) }
119. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); self.where_clause.0.walk_ast(out)?; Ok(()) }
120. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); self.where_clause.0.left.walk_ast(out)?; out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
121. out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); self.where_clause.0.left.walk_ast(out)?; out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
122. out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); self.where_clause.0.left.walk_ast(out)?; out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
123. out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); self.where_clause.0.left.walk_ast(out)?; out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
124. out.push_sql(" WHERE "); self.where_clause.0.left.walk_ast(out)?; out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
125. out.push_sql(" WHERE "); users::table.walk_ast(out)?; out.push_sql("."); out.push_identifier("id"); out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
126. out.push_sql(" WHERE "); users::table.walk_ast(out)?; out.push_sql("."); out.push_identifier("id"); out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
127. out.push_sql(" WHERE "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_identifier("id"); out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
128. out.push_sql(" WHERE "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_identifier("id"); out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
129. out.push_sql(" WHERE "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
130. out.push_sql(" WHERE "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(" = "); self.where_clause.0.right.walk_ast(out)?; Ok(()) }
131. out.push_sql(" WHERE "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(" = "); out.push_bind_param( &self.where_clause.0.right.item)?; Ok(())
132. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); self.distinct.walk_ast(out)?; self.select.walk_ast(&self.from, out)?; out.push_sql(" FROM "); self.from.walk_ast(out)?; self.where_clause.walk_ast(out)?; Ok(()) }
133. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(", "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("name"); out.push_sql("\""); out.push_sql(" FROM "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql(" WHERE "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\""); out.push_sql(" = "); out.push_bind_param(&self.where_clause.0.right.item, out)?; Ok(()) }
134. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { out.push_sql("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\"");
135. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { if let AstPass::ToSql(ref mut builder) = out { builder.push_sql("SELECT "); } out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\"");
136. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { let AstPass::ToSql(ref mut builder) = out; builder.push_sql("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\"");
137. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { let AstPass::ToSql(ref mut builder) = out; builder.push_sql("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\"");
138. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { let AstPass::ToSql(ref mut builder) = out; builder.sql.push_str("SELECT "); out.push_sql("\""); out.push_sql("users"); out.push_sql("\""); out.push_sql("."); out.push_sql("\""); out.push_sql("id"); out.push_sql("\"");
139. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { let AstPass::CollectBinds { collector, metadata_lookup } = out; collector.push_bound_value( &self.where_clause.0.right.value, metadata_lookup, )?; Ok(()) }
140. fn walk_ast(&self, out: AstPass) -> QueryResult<()> { Ok(()) }
141. These optimizations are what let us build zero cost abstractions
142. pub struct HashSet<K> { map: HashMap<K, ()> } impl<K: Hash + Eq> HashSet<K> { pub fn insert(&mut self, value: K) { self.map.insert(value, ()); } pub fn contains(&self, value: &K) -> bool { self.map.contains_key(value) } }
143. pub struct HashSet<K> { map: HashMap<K, ()> } impl<K: Hash + Eq> HashSet<K> { pub fn insert(&mut self, value: K) { self.map.insert(value, ()); } pub fn contains(&self, value: &K) -> bool { self.map.contains_key(value) } }
145. Please ask me questions now
146. Contact • twitter: @sgrif • github: @sgrif • podcast: bikeshed.fm