If constants are the default for the := operator, why the const keyword?

[ThatXliner]

I've read the docs (which are super great by the way) which said that constant variables are the default when declaring variables (and assigning). So why do you need "const" if mutability is opt-in?

[JalonSolov]

Immutable variables are the default, not constant variables... there's no such thing as a constant variable (those 2 words mean pretty much the opposite).

consts can only be initialized at compile time, and there are optimizations that can be performed because of that.

Immutable variables are initialized at runtime, but cannot be changed afterwards.

Mutable variables can be changed as much as you like.

[ThatXliner]

Ohhhhh, so it's kind of like Nim. Got it! Thanks!

If I'm not mistaken (I'm still learning C++ 😅), that's kind of like C/C++'s macro

#define PI 3.1415

[JalonSolov]

Effectively similar on the surface, but very different in the internals of the compiler. :-) const declarations have actual types, etc. where a macro is basically just a text replacement.