Re: Template mixins and struct constructors

[Daniel Kozak via Digitalmars-d-learn]

On Wednesday, 2 March 2016 at 14:50:15 UTC, Adrian Matoga wrote:

On Wednesday, 2 March 2016 at 14:36:59 UTC, Daniel Kozak wrote:

OK maybe this one:

template AddField(T) {
    T b;
    this(Args...)(T b, auto ref Args args)
    {
           this.b = b;
       this(args);
    }
    this(int a) {
        this.a = a;
    }
}

struct Bar {
    int a;
    mixin AddField!(string);
}

unittest {
    auto bar1 = Bar(5);
    auto bar2 = Bar("bar", 15);
}

Then it's limited to structs in which only "int a" is to be initialized. Not very useful and the templated ctor is not needed now.

struct Baz {
    mixin AddField!string; // fail, no "int a" in Baz.
    ulong d;
    double x;
    string foo;
}

OK then:

mixin template AddField(T) {
    T b;
    auto ref constructor(Args...)(T b, auto ref Args args)
    {
        typeof(this) r;
        r.b = b;
        r.__ctor(args);
        return r;
    }
}

struct Bar {
    mixin AddField!string;
    int a;
    this(int a) { this.a = a; }
    alias __ctor = constructor;
}

unittest {
    import std.stdio;

    auto bar1 = Bar(5);
    auto bar2 = Bar("bar", 15);
    writeln(bar1);
    writeln(bar2);
}