(a = b)

Understanding type inference and equality in Rust

This medium-difficulty Rust question tests your grasp of type inference and how the language resolves types when equality constraints are involved. It's the kind of question that separates candidates who have read Rust syntax from those who understand how the compiler reasons about types.

To approach problems like this, you need to trace how Rust's type checker propagates constraints through an expression. When you write code that asserts or implies equality between values, the compiler uses bidirectional type checking to unify their types. The key is understanding what information flows in each direction and which type wins when there is ambiguity.

• Type inference and unification
• Equality constraints and type propagation
• Implicit vs. explicit type annotation
• Compiler error messages as debugging tools