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Comment by hellofunk | Hacker News Reader

The discussion about shadowing variables doesn’t seem to make a very good case to me about this feature. Why would you want to introduce all those variables on the stack, each of a different type (even if they have the same name, presumably they are new pieces of stack memory)? Why not just mutate an existing variable each time?

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Sometimes you need a different type and you don't care about the intermediate values. Parsing a string into an integer is a good example. Once you have the integer, generally you don't care to use the string anymore.

  let num = String::from("10");
  let num: i32 = num.parse().unwrap();

For me, understanding shadowing adds to one's understanding of what 'let' means. Whether the shadowed variables each get new memory I'd be happy to leave to the compiler/optimiser.

Each variable is of one type. If you change the type, you must declare a new variable.

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