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