On Wednesday, 4 December 2019 at 14:44:43 UTC, Ola Fosheim
Grøstad wrote:
When is there a noticable difference when using const values
instead of immutable values in a function body? And when should
immutable be used instead of const?
f(){
const x = g();
immutable y = g();
... do stuff with x and y …
}
There is a difference I guess if g() returns a reference type and
is an inout function. immutable y will only work if the reference
returned is immutable.
Const is a promise to the rest of the code that you will never
mutate it. Immutable is a promise by the rest of the code that it
will never mutate.
Immutable is more powerful, allowing data sharing in overlapping
slices and between threads without locks. Const is more
versatile, allowing references to data regardless of its
mutability.
So if g() always returns immutable, it’s best to receive it as
such, not const. If it can be either, it must be received as
const.
I'm comparing D to C++ and I get the following mapping:
Does that make sense at all? D’s const is transitive, C++’s is
not.
Bastiaan.
