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In actuality it will be extremely obvious in the IDE and the developer would not make this error.

if "val" is a constant, and you try to mutate it later, the compiler will tell you, "That ain't gonna happen."

In many cases, you would get warnings when accessing a var that you don't get when accessing a val. Also, IntelliJ suggests converting to val if a var is never reassigned.

As others said, not a problem if you are using an IDE (and a specific one.)

Considering who authored the language, I am not surprised at all.