The const
and final
keywords in Dart are used to declare variables that cannot be reassigned after they have been initialized. However, there is a subtle difference between the two keywords:
const
: Theconst
keyword is used to declare variables that are compile-time constants. This means that the value of aconst
variable must be known at compile time and cannot be changed during runtime. In addition,const
variables are implicitlyfinal
and must be set to a value that is also aconst
, such as a string, number, or constant expression.final
: Thefinal
keyword is used to declare variables that are runtime constants. This means that the value of afinal
variable can be set at runtime, but cannot be changed after it has been initialized. Unlikeconst
variables,final
variables can be set to values that are notconst
, such as the result of a function call or a user-input value.
In general, you should use the const
keyword when you need to declare a value that must be constant at compile time and the final
keyword when you need to declare a value that can be set at runtime but cannot be changed after it has been initialized. If you are not sure which keyword to use, it is usually safe to use final
.