What is the difference between `let` and `var` in swift?

Question

What is the difference between let and var in Apple\'s Swift language?

In my understanding, it is a compiled language but it does not check

Answer 1

Though currently I am still reading the manual, but I think this is very close to C/C++ const pointer. In other words, something like difference between char const* and char*. Compiler also refuses to update content, not only reference reassignment (pointer).

For example, let's say you have this struct. Take care that this is a struct, not a class. AFAIK, classes don't have a concept of immutable state.

import Foundation


struct
AAA
{
    var inner_value1    =   111

    mutating func
    mutatingMethod1()
    {
        inner_value1    =   222
    }
}


let aaa1    =   AAA()
aaa1.mutatingMethod1()      // compile error
aaa1.inner_value1 = 444     // compile error

var aaa2    =   AAA()
aaa2.mutatingMethod1()      // OK
aaa2.inner_value1 = 444     // OK

Because the structs are immutable by default, you need to mark a mutator method with mutating. And because the name aaa1 is constant, you can't call any mutator method on it. This is exactly what we expected on C/C++ pointers.

I believe this is a mechanism to support a kind of const-correctness stuff.