Re: Template method and type resolution of return type

[matovitch via Digitalmars-d-learn]

On Saturday, 19 April 2014 at 18:46:28 UTC, matovitch wrote:

On Saturday, 19 April 2014 at 17:49:54 UTC, bearophile wrote:

matovitch:

struct Test
{
        immutable (ubyte)[] data;

        T get(T)()
        {
                return *(cast(T*)(&(data[0])));
        }

It's better to return const/immutable data. Otherwise the program gives undefined results. In alternative use mutable ubytes for data.

Also &data[0] is probably data.ptr.

I did'nt know that one.

This won't compile :

import std.stdio;

void main()
{
        Test t;
        t.data = [152, 32, 64, 28, 95];
        float b = t.get;
        writefln("%s", b);

D doesn't perform inference on the return type.

I see. But why ?

It's seems it exits a workaround overloading cast operators in c++ : http://programmaticallyspeaking.blogspot.se/2012/09/infer-return-type-for-templated.html

However I think it would only work with opImplicitCast in D. The code given in vibe.d doc could became :

void manipulateJson(Json j)
{
        j = Json.emptyObject;
        j.name = "Example";
        j.id = 1;

        // retrieving the values is done using get()
        assert(j["name"] == "Example");
        assert(j["id"] == 1);

        // print out as JSON: {"name": "Example", "id": 1}
        writefln("JSON: %s", j.toString());
}

ps : Thank you for all your great examples on Rosetta code (or the last one about the rubik's cube).

Or even :

void manipulateJson(Json j)
{
        j = Json.emptyObject;
        j.name = "Example";
        j.id = 1;

        assert(j.name == "Example");
        assert(j.id == 1);

        // print out as JSON: {"name": "Example", "id": 1}
        writefln("JSON: %s", j.toString());
}

Or at least this will work :

void manipulateJson(Json j)
{
        j = Json.emptyObject;
        j.name = "Example";
        j.id = 1;

        string s = j.name;
        assert(s == "Example");


        // print out as JSON: {"name": "Example", "id": 1}
        writefln("JSON: %s", j.toString());
}

Ok I stop fooding.