var, final, and const Explained

In Dart you store data in named boxes called variables. The keyword you pick decides whether that box can ever change.

Use var when a value will change later. Dart still figures out the type for you, so var is convenient and safe.

Even though var looks loose, the type is fixed once. Assign an int and you cannot later store text in the same box.

Use final when a value is set once and never reassigned. It is decided while your program runs, then stays put.

Try to give a final a new value and Dart stops you at compile time. This protects values you never meant to change.

Use const for values known before the program even runs. They are baked in at compile time, fixed forever.

A const value must be computable while compiling. You cannot use something only known at run time, like the current clock.

Think of it this way: final is set once at run time, while const is frozen even earlier, at compile time. 🧊

A good habit is reaching for final first. If a value never needs to change, final makes your intent clear and prevents bugs.

Two identical const objects are shared as the same instance in memory. This saves space and is great for fixed config values.

Will it change? Use var. Set once at run time? Use final. Known before running? Use const. That single question guides you.

Pick the keyword for a value computed at run time but never reassigned.

You learned that var can change, final is set once at run time, and const is frozen at compile time. Reach for final by default. 🎉