CTE Functions

A function is CTE if:

It is marked with const modifier
It is possible to infer that function can be CTE

We mark a function as CTE so.

const func foo() {}

Then the compiler will check that all computations performed inside this function 'foo' are CTE, if not, it gives an error.

In another way, the result of the function won't be inlined in usage places, but it is possible to use a function that wasn't qualified as const in a CTE context. More about that below.

const inference

Another approach is more complex for the compiler but simple for the user: If we declare a function and use it in CTE context when compiler goes to this function and checks that it's CTE function. Anyway, if we use this function in a run-time context it won't be inlined and evaluated at compile-time. Example.

// Just a simple function that returns `1`
func foo = 1

const func myConstFunc {
    const a = foo()
}

func myRawFunc {
    let a = foo()
}

After const expansion this code will look (structurally) like that.

func foo() = 1

const func myConstFunc() {
    const a = 1
}

func myRawFunc() {
    let a = foo()
}

As you can see in myRawFunc foo is still a function call, because foo used in a non-const context. Whereas in myConstFunc value returned by foo was inlined as we declared a as const. const qualifier does not mean that everything inside it will be inlined, you still can declare let or use if inside of it. const just means the compiler will check function for constness and tell you if it's not.

const inference​

const inference