Re: Newbie: copy, assignment of class instances

[bearophile]

Larry Luther:
>     void copy (in A a) {

In D2 it's better to use "const" or "immutable" instead of "in".

Here's one version of the code const-aware:


import std.stdio: writeln;
import std.string: format;


template ExceptionTemplate() {
    this() {
        super(this.classinfo.name);
    }

    this(string msg) {
        super(this.classinfo.name ~ ": " ~ msg);
    }
}


class ArgumentException: Exception {
    mixin ExceptionTemplate;
}


class A {
    int x, y;

    this(int xx, int yy) {
        this.x = xx;
        this.y = yy;
    }

    void copyFrom(const Object other) {
        const o = cast(typeof(this))other;
        if (o is null)
            throw new ArgumentException("Some message here...");
        x = o.x;
        y = o.y;
    }

    override string toString() const {
        return format("A(%d, %d)", this.x, this.y);
    }
}


class B : A {
    int z;

    this(int xx, int yy, int zz) {
        super(xx, yy);
        this.z = zz;
    }

    override void copyFrom(const Object other) {
        const o = cast(typeof(this))other;
        if (o is null)
            throw new ArgumentException("Some message here...");
        super.copyFrom(other);
        z = o.z;
    }

    override string toString() const {
        return format("B(%d, %d, %d)", this.x, this.y, this.z);
    }
}


void main() {
    B foo = new B(1, 2, 3);
    B bar = new B(4, 5, 6);

    writeln("foo = ", foo);
    writeln("bar = ", bar);

    foo.copyFrom(bar);

    writeln("foo = ", foo);
    writeln("bar = ", bar);
}


Bye,
bearophile