Use let instead of var: When you know that a variable won’t change, declare it as a constant using let. This allows the Swift compiler to make optimizations.

In Swift, the let keyword is used to declare a constant, which means the value it holds cannot be changed once it is set. This immutability allows the Swift compiler to make certain optimizations.

Value Propagation: If a constant is initialized with a literal value or a simple expression, the compiler can replace uses of the constant with its initial value. This is known as constant propagation. This can eliminate unnecessary memory accesses and computations.

Dead Code Elimination: If a constant is initialized but never used, the compiler can eliminate the code that initializes the constant. This is known as dead code elimination. This can reduce the size of the compiled code.

Memory Layout Optimization: The compiler can make assumptions about the memory layout of structures and classes that contain constants. For example, it can place constants next to each other in memory, which can improve cache locality and reduce memory usage.

Thread Safety: Constants are inherently thread-safe, because they cannot be changed after they are initialized. This means the compiler doesn’t need to generate code to synchronize access to constants, which can improve performance in multithreaded code.

Remember, these optimizations are automatic and transparent. You don’t need to do anything special to enable them, other than using let to declare constants whenever possible.