Enforce immutability

[nschurmann]

Is there a way to enforce immutability? I know that the team chose to use var instead of scoped variables like const and let, but it would be nice for the compiler to detect if there has been a re-assignation and show an error at compile time to prevent it.

[GeoffreyBooth]

I think #4985 is the main issue discussing supporting const. Basically it’s not supported currently, but there are ways that support could be added (like via new syntax such as := instead of =); however there’s debate as to whether this violates the spirit of CoffeeScript where one of the original tenets was that you shouldn’t need to think about whether a variable is being declared versus assigned.

[nschurmann]

The way I see this that may not violate the "const" assignment is that we keep using var, however, internally coffeescript could have a reference of all the variables that have been declared, if the variable has more than one assignment then show a warning or error during compilation. IMO I don't care if I'm using var, let or const, I just don't want to assign a value to a variable more than once. So I see it as a feature of coffeescript rather than a transpilation option.