Type Annotations That Help

A type annotation states a value's type right in the declaration, so both you and Mojo know exactly what it holds.

Add a colon and the type after the name. Here : Int promises that count will only ever hold whole numbers.

Without an annotation Mojo infers the type from the value. Writing it yourself makes your intent explicit and clear.

An annotation lets Mojo reject a wrong value at compile time. Assigning text to an Int becomes an immediate error.

Knowing the exact type ahead of time, Mojo can generate faster machine code instead of checking types as it runs.

Annotations work for every type. Spell out Float64 or Bool to document precisely what each value is.

Mark text values with String so readers instantly see that a var carries words rather than numbers.

A type next to a name tells the next reader, including future you, what to expect without hunting for the value.

Strict fn functions require type annotations on their parameters, which is where this habit pays off most.

Even when inference works, annotate the values others rely on. Clear types at boundaries prevent confusion across your code.

Annotations turn silent bugs into loud errors and unlock speed. A little typing now saves real debugging later.

You annotate a var as Int but try to assign it the text "oops". What happens in Mojo?

A type annotation names a value's type with a colon, catching errors early and helping Mojo run faster. 🎯