Re: Calls to struct methods and immutable

[bearophile]

Joseph Rushton Wakeling:

      auto foo = cast(immutable) Foo(3, 4);

Strive to write D code as much cast-free as possible, because
they are dangerous.

The reason seems pretty evident -- making the instance immutable means that the temporary internal variable c in check() can't be (over)written.

You are wrong. A version of your code:


import std.math;

struct Foo {
     int a, b;

/*
     this(int a, int b) {
         this.a = a;
         this.b = b;
     }
*/

     void check() const pure nothrow {
         immutable real p = a ^^ 2 + b ^^ 2;
         assert(sqrt(p) < 10);
     }
}

void main() {
     auto foo = immutable(Foo)(3, 4);
     // immutable foo = Foo(3, 4); // simpler alternative
     foo.check();
}


Bye,
bearophile